Copy Attacks vs Discard Energy Interactions

[admin]

As some of you might know, we have an ongoing issue involving copy attacks (Metronome, Foul Play, etc) vs discarding self energy. And I want to fix it once and for all.

Copy Attack Examples

(1) Metronome (errata’d): Choose 1 of the Defending Pokémon’s attacks. Metronome copies that attack except of its Energy costs. You must still do anything else required to use that attack, such as discarding Energy cards. (No matter what type the Defending Pokémon is, Clefairy’s type is still Colorless).

(2) Foul Play: Choose 1 of your opponent’s Active Pokémon’s attack and use it as this attack.

(3) Copy: Choose 1 of the Defending Pokémon’s attacks. Copy copies that attack. This attack does nothing if Sudowoodo doesn’t have the Energy necessary to use that attack. (You must still do anything else required in order to use that attack.)

Discarding Attack Examples

(A) Fire Spin: 70 damage. Discard 2 basic Energy cards attached to Flareon or this attack does nothing.

(B) Flamethrower: 50 damage. Discard a [R] Energy card attached to Arcanine in order to use this attack.

(C) Thunderbolt: 50 damage. Discard all Energy cards attached to Pikachu in order to use this attack.

(D) Discharge: 30× damage. Discard all [L] Energy cards attached to Flaaffy in order to use this attack. Flip a number of coins equal to the number of [L] Energy cards you discarded. This attack does 30 damage times then number of heads.

(E) Victory Ball: 50 damage. Discard a [R] Energy attached to this Pokémon.

The Question

What should happen in each case if the energies to be discarded in the attack text are NOT present on the attacker who copies the attack? (please mention in detail if there are more than one possibility for each case)**

There are 15 total cases to cover. Please reply by selecting & clicking “quote” & filling this table;

	A	B	C	D	E
1
2
3

[admin]

Hi @Testers I want to fix Clefable metronome issue but I got confused with legacy vs modern text & interpretation of energy discards across different generations. I also want to normalize the internal functions as much as I can and have these interactions work nicely in Unlimited too. Can you help me figure out all the copy attack requirement handling, by filling out the table above?

[JasonKlaczynski]

A1: The attack would have no effect.

A2: The attack would have no effect. (This one is tricky because it is assuming the Japanese translation was correct.)

A3: The attack would have no effect.

B1: The attack would have no effect.

B2: The attack would fail. (This is because Foul Play must meet requirements that read in order to use this attack or or this attack does nothing.) [Revised.]

B3: The attack would have no effect.

C1–C3: In the event of some rare interaction where the Pokémon copying the attack was able to attack for 0 Energy, this attack would fail, since discarding all Energy means you have to discard at least one Energy.

D1–D3: The attack would have no effect if there were no Lightning Energy to discard.

E1: The attack would work because this attack appear in a newer era without any “in order to” or “or this attack fails” clause. A Fire Energy would only be discarded if one was attached to the attacking Pokémon. (This would include cards like Rainbow Energy.) [Revised.]

E2: The attack would work. A Fire Energy would only be discarded if one was attached to the attacking Pokémon. (This would include cards like Rainbow Energy.)

E3: The attack would work because this attack appear in a newer era without any “in order to” or “or this attack fails” clause. A Fire Energy would only be discarded if one was attached to the attacking Pokémon. (This would include cards like Rainbow Energy.) [Revised.]

Simple summary: Metronome and Copy are simple; you must make the discard requirements for the attacks to work. Foul Play is trickier in that you don’t have to make the discard requirement unless the attack has a disclaimer text that the attack does nothing if you can’t meet the requirement. However, another tricky aspect of this is that this text can be disregarded for WotC era cards, including ones that say “Use this attack only if there are R Energy…” The reason for this is that text was added only to compensate for the mistranslation of Metronome.

Also noteworthy: When attack says you must discard all of a specific type of Energy (for example, discard all Lightning Energy), you must discard at least one of those types of Energies for Metronome and Copy to be able to use it. Foul Play is different.

These are some of the trickiest rulings in Pokémon (particularly when mixing eras together) so it’s possible I am wrong on one or more of them, but based on everything I know at the moment, the above chart should be accurate. I will provide updates if I learn differently.

[dxdydzd]

A2 is correct; in fact the ruling from the Compendium specifically mentions the phrase “or the attack does nothing”.

Q. Do I have to meet the energy requirements for the attack I choose with Zoroark’s “Foul Play”?
A. No, you do not have to meet the energy requirements for the attack. However, if the attack says you must do something or the attack does nothing, that part still has to be done. (Black & White FAQ; Apr 28, 2011 PUI Rules Team)

For B2, the attack would do nothing, just like A2. “In order to use this attack” is the old wording that got replaced by “or this attack does nothing”. An example showing they are the same:
Ponyta RO’s Ember: Discard 1 {R} Energy card attached to Ponyta in order to use this attack.
Japanese Ponyta’s Ember: このカードについている「炎」エネルギーカードを1枚トラッシュする。(トラッシュできない時、このワザのダメージは0になる)
Entei N3 6’s Searing Flames: Discard 2 {R} Energy cards attached to Entei or this attack does nothing.
Japanese Entei’s Searing Flames: 自分についている「炎」エネルギーカードを2枚トラッシュする。(トラッシュできないとき、このワザのダメージはなくなる。)

Ember is “in order to use this attack”, Searing Flames is “or this attack does nothing”, but in Japanese they are both 「このワザのダメージはなくなる」. 0 and なく mean the same thing here; なく is seen on later cards because it can also be used to refer to effects doing nothing, not just damage (for example, Corsola N2’s Recover includes the text 「この効果はなくなる」).

For E1 and E3, the attack would do damage even if you can’t discard Energy. With this wording, the Energy discard is an effect, not a cost. The attack does not fail because you were unable to pay a cost; instead, you do as much as you can, and since you have no [R] Energy attached, you discard nothing.

Compendium entry:

Q. If I use “Metronome” and copy Lugia-EX’s “Elemental Blast” attack, do I have to discard a Fire, Water and/or Electric energy if I have any of them attached?
A. Yes, when using Metronome in this fashion you do as much of it as you can. So if Clefable-EX only has two Water energy attached, you have to discard one of the Water energy cards (but not both). And if you have a basic Water Energy and a Rainbow Energy attached, you would have to count the Rainbow as one of the other types and discard both cards. (May 4, 2006 PUI Rules Team)

My summary for all this would be that while Metronome and Foul Play ignore Energy costs, all three “copy” attacks are subject to having to pay any additional costs or meet additional restrictions in order for the attack to succeed. The difficult part is identifying what is a cost or requirement and what is merely an effect.

The phrases “in order to”, “if you can’t/don’t, this attack does nothing”, “or this attack does nothing” are all signs that the preceding portion is a cost. In fact this extends to Abilities and Trainers too: Radiant Greninja’s Concealed Cards uses “in order to”, Holon Supporters use “if you can’t”, and both are ruled to be costs!

Q. When using Radiant Greninja’s “Concealed Cards” Ability, can I discard an Energy card from my hand if there are no cards left in my deck?
A. No, discarding an Energy card is a cost (as identified by the “in order to” phrase) so you can’t do it if you can’t do the actual effect of the card.

Q. Can you play Holon Scientist if you will not be able to draw any cards?
A. No, you must be able to draw at least one card after you have paid the discard cost. (Jan 4, 2007 PUI Rules Team)

Magby TR even gets a ruling for “copying” Supporters: you must pay costs in order to get the Supporter effect.

Q. If I play a Holon trainer supporter and then use Magby’s “Detour” attack, do I have to discard a card to do Detour?
A. Yes, you would have to discard a card in order to use Detour in this particular situation. (Dec 15, 2005 PUI Rules Team)

Requirements have not been brought up in this thread yet, but they are relevant for handling “copy” attacks. These would include things like “you can only use this attack if/when” or “you can’t use this attack unless”. Requirements, like costs, are also present on Supporters, as seen in this other Magby ruling:

Q. If I use Magby’s “Detour” attack to use the effect of a Supporter card in play, do I have to meet all the requirements of that Supporter? For instance, if I want to Detour a Steven’s Advice do I have to have less than 7 cards in my hand at that time? Or do I have to shuffle in a card when Detour’ing Bill’s Maintenance?
A. You can use Detour, but you must still meet all requirements that are necessary to play the card normally (except for the supporter rule). If you don’t or can’t meet those restrictions, the effect fails. (Dec 15, 2005 PUI Rules Team)

An example of something that is NOT a cost is the plain “discard an Energy attached to this Pokémon” without any of the key phrases mentioned earlier. “You may (effect). If you do, (effect).” is another; similar to “in order to”, this wording is found on Abilities too:

Q. Can I use Zoroark GX’s “Trade” Ability to discard a card from my hand if there are no cards left in my deck?
A. Yes you can. The first part of Trade is to discard a card from your hand, period. Then you do as much of the rest of the Ability as you are able to.

Moltres FO in particular uses the “You may (effect). If you do, (effect).” wording, which is why in pre-Neo formats, you flip for Confusion before discarding for Moltres, but discard before flipping for Charizard.

• Clarification on the whole Moltres WildFire/Confusion thing. When flipping for confusion, you must pay all Attack Costs BEFORE you flip for confusion. This means anything that is written as “IN ORDER TO DO THIS ATTACK” (such as Charizard’s Fire Spin: Discard 2 Fire Energy card attached to Charizard IN ORDER TO use this attack). However, anything that does not state IN ORDER TO gets done AFTER the Confusion flip. This means for Moltres’ Wildfire you do NOT discard cards for the effect of the attack until AFTER you see if the attack even occurs. (Mar 30 WotC Chat)

[JasonKlaczynski]

@dxdydzd has made some great corrections that take into consideration that newer cards interaction differently with older cards than other older cards from the same era did. (Great job pointing these out. I’ve edited my post to reflect your corrections.)

However, I must caution (as I always have) that I believe attempting to have a fully functional Unlimited format is in vain. Unlimited is full of extremely complicated interactions, many of which there are no official rules for. Given that TCG ONE for years has struggled to achieve bug-free formats even for the oldest and simplest formats, I would urge @admin and his developers to leave Unlimited as the lowest priority format.

[dxdydzd]

Another case of Energy discarding that wasn’t in the OP is discards that happen on a coin flip. There are a lot of different cases for this, and how to resolve them depends on the format and even the region.

To start with, let’s look at Torchic RS 73’s Fireworks:

Flip a coin. If tails, discard a {R} Energy card attached to Torchic.

If you copy this attack, flip tails, and can’t discard an [R] Energy, you don’t, but the attack still does its damage. This is similar to Lugia ex’s Elemental Blast; the discard is an effect and not a cost, since it doesn’t have the magic words “in order to”, “if you can’t”, or “or this attack does nothing”.

Now consider Charmeleon SW’s Flare Tail:

Flip a coin. If heads, discard a {R} Energy attached to Charmeleon and this attack does 50 damage plus 20 more damage.

What happens if you copy it, flip heads, but can’t discard an [R] Energy? The discard and bonus damage are both effects, not costs, so we follow the principle of “do as much as you can”: you would get the bonus damage and not have to discard. It feels like cheating, but the same sort of “cheating” is allowed even when you don’t flip to discard (Elemental Blast), so we kind of have to let it go.

This was handled very differently in Base-Neo. Here’s Cyndaquil N1’s Fireworks (which, incidentally, shares a name with Torchic’s attack):

Flip a coin. If tails, discard 1 Energy card attached to Cyndaquil.

If you copy it, flip tails, and can’t discard an Energy, the attack fails, unlike Torchic’s Fireworks where you still get the damage. The Japanese wording makes it clearer:

コインを投げて「うら」なら、自分についている「エネルギーカード」を1枚選び、トラッシュする。トラッシュできないとき、このワザのダメージはなくなる。 (If you can’t discard, this attack does no damage.)

In Base-Neo, almost all attacks that tell you to discard Energy attached to that Pokémon will fail if you are unable to discard. This applies even if the text is missing “in order to” or “or this attack does nothing”. Some of these instances of missing text were the result of WotC neglecting to translate the Japanese reminder text (like the Cyndaquil above), but others had missing text even in their Japanese prints. This site lists some examples, calling attention to Blaine’s Ninetales G2 and Lt. Surge’s Raichu G2:

コインを投げて「うら」なら、自分についている「炎」エネルギーカードを、すべてトラッシュする。(Flip a coin. If tails, discard all {R} Energy cards attached to Blaine’s Ninetales.)

Notice that the 「トラッシュできないとき、このワザのダメージはなくなる」 portion is missing.

The exception to this “no discard = attack fails” rule is Dark Houndoom N4.

If there are any {D} Energy cards attached to Dark Houndoom, discard 1 of them and this attack does 30 damage plus 20 more damage (plus 10 more damage for the {D} Energy you discarded). If there aren’t any, this attack does 30 damage.

The Japanese text uses 「この効果はなくなる」, meaning “this effect does nothing” — note the usage of 効果 (effect) instead of ダメージ (damage). In this case the attack doesn’t fail completely; only the additional effect does, and you still get the base damage of 30.

What about the Base-Neo equivalent of Charmeleon SW’s Flare Tail, an attack that does discard + bonus damage on a flip? I’ll use Dark Flareon RO’s Playing with Fire as an example:

Use this attack only if there are any {R} Energy cards attached to Dark Flareon. Flip a coin. If heads, discard 1 of those Energy cards and this attack does 30 damage plus 20 more damage; if tails, this attack does 30 damage.

It says right there that you can only use it if there are [R] Energy cards attached, so you can’t copy it if that’s not the case, right? Well, the Japanese text tells a completely different story:

コインを投げて「おもて」なら、20ダメージを追加して、このカードについている「炎」エネルギーカードを1枚トラッシュする。(トラッシュできない時、このワザのダメージは0になる) (Flip a coin. If heads, this attack does 20 more damage and discard a [R] Energy card attached to this card. (If you can’t discard, this attack does 0 damage.))

(Notice that unlike Dark Houndoom, Dark Flareon uses ダメージ instead of 効果.)

What this means is that under the Japanese wording, if you don’t have [R] Energy attached, you can still copy Playing with Fire. If you flip heads, you do 0 damage, because you can’t discard [R]. If you flip tails, you do 30 damage. Under the English wording, if you don’t have [R] attached, you can’t copy Playing with Fire.

A rather amusing example of both Japan and the West getting it wrong is Blaine’s Charmander G2. This sounds crazy; if both sides got it wrong, how do we know what’s right? Have a look at the English and Japanese texts and see if you can figure out on your own:

Use this attack only if there are any {R} Energy cards attached to Blaine’s Charmander. Flip a coin. If tails, discard 1 of those cards.

コインを投げて「うら」なら、自分についている「炎」エネルギーカードを1枚選び、トラッシュする。 (Flip a coin. If tails, discard a [R] Energy card attached to Blaine’s Charmander.)

The answer is that the English text unnecessarily adds the “use this attack only if” requirement similar to Dark Flareon, and the Japanese text lacks 「トラッシュできないとき、このワザのダメージはなくなる」 (the attack fails if you can’t discard).

[JasonKlaczynski]

So the question ultimately posed is this: following the proper translation of Metronome, what happens when Metronome copies Blaine’s Charmander’s Play with Fire attack?

If Clefairy or Clefable had a Fire Energy attached and flipped Tails for this attack, we know that the Fire Energy would be discarded. But since the discard only happens on a coin flip, can this attack be used without a Fire Energy? And if so, would the attack still work on Tails?

If these type of coin flip discard attacks functioned consistently throughout the Base to Neo era, we could assume Neo Cyndaquil’s attack was clarifying something that existed before, and that if Metronome couldn’t discard a Fire Energy for Play with Fire, the attack would fail. However, what I’ve learned over the years researching these old cards is that their functionalities are often arbirtrarily inconsistent, and you need rulings for specific cards.

At the end of the day, these are trivial rulings, and they serve more as interesting trivia than anything. Without an official ruling, my recommendation would be to code the functionality of these attacks based on the literal Japanese text of each card. That would be as follows:

• Blaine’s Charmander’s Play with Fire: Metronome can always copy this attack, and only on Tails must it discard a Fire Energy. If the discard cannot be met, the attack still deals 20 damage.

• Dark Flareon’s Play with Fire: Metronome can always copy this attack, but the attack will fail if Clefairy/Clefable cannot discard the Fire Energy on Heads (as the Japanese text clarifies).

I believe the Copy attacks from future generations should function the same way, but I’m less concerned about these since at that point even the game’s designers seem to be guessing what their own rulings would be.

[dxdydzd]

Blaine’s Charmander is listed as one of the cards that should have “if you can’t discard, this attack does nothing” on the site I linked.

ヒトカゲ(第1弾)

オリジナル
炎無 ひのこ 30
自分の「炎」エネルギーカードを1枚はがしてすてる。

オラクル
炎無 ひのこ 30
自分についている「炎」エネルギーカードを1枚トラッシュする。トラッシュできないとき、このワザのダメージはなくなる。

他：リザード(第1弾)の「かえんほうしゃ」、リザードン(第1弾)の「ほのおのうず」、キュウコン(第1弾)の「だいもんじ」、ウィンディ(第1弾)の「かえんほうしゃ」、ブーバー(第1弾)の「かえんほうしゃ」、カツラのヒトカゲ(カツラ)の「ファイヤーテール」、カツラのキュウコン(ジム拡張2)の「しゃくねつ」、マチスのライチュウ(ジム拡張2)の「バリバリ」(Blaine’s Charmander’s Fire Tail, which was translated as Fire Tail Slap in English)

The source given for this errata is the 『ポケモンカードオフィシャルブック2000』.

[JasonKlaczynski]

Nice find! Given that, if we go by the literal text, we would still allow Metronome (and Copy) to use this attack without Fire Energy, but the attack would fail on Tails, then.

[dxdydzd]

Yes, that is correct. (Just like Dark Flareon, but with heads/tails reversed.)

[dxdydzd]

So, I did a bit more digging on this topic, because Shiftry ex’s Skill Hack seems to contradict Clefable ex’s Metronome:

Q. If I use Shiftry-EX’s “Skill Hack” attack and copy an attack like Salamence-EX’s “Hydro Wave” or Steelix-EX’s “Mudslide”, do I have to have any Water energy or Fighting energy attached to Shiftry-EX or not?
A. Basically when it comes to statements like “discard X Energy”, they are considered necessary to use that attack. So for Hydro Wave Shiftry-EX would need to have at least one Water energy to discard, and for Mudslide Shiftry-EX would need to have two Fighting energy to discard. If you can only choose an attack that has requirements and you don’t have the correct energy cards attached, then the Skill Hack attack does nothing. (Mar 15, 2007 PUI Rules Team)

Q. If I use “Metronome” and copy Lugia-EX’s “Elemental Blast” attack, do I have to discard a Fire, Water and/or Electric energy if I have any of them attached?
A. Yes, when using Metronome in this fashion you do as much of it as you can. So if Clefable-EX only has two Water energy attached, you have to discard one of the Water energy cards (but not both). And if you have a basic Water Energy and a Rainbow Energy attached, you would have to count the Rainbow as one of the other types and discard both cards. (May 4, 2006 PUI Rules Team)

Why the inconsistency? Why can Clefable ex copy Elemental Blast if it doesn’t have the Energy to discard, but Shiftry ex not copy Mudslide if it doesn’t have the Energy to discard? Elemental Blast says “discard X Energy” (granted, it’s 3 different types), so should that not also be considered necessary to use it? To add to the confusion, years later in BW, Zoroark’s Foul Play reversed the Shiftry ex ruling and functioned like Clefable ex’s Metronome instead:

Q. If Zoroark uses “Foul Play” to copy Reshiram’s “Blue Flare” attack, what happens if I don’t have have any Fire Energy attached to Zoroark?
A. The damage amount is done regardless of whether Zororark has any Fire Energy attached to it or not, but if you have one or two Fire Energy attached to Zoroark you must discard them. (Black & White FAQ; Apr 28, 2011 PUI Rules Team)

How do we reconcile all this? The best explanation I have found is that Energy discard rules when copying attacks differ based on the format. Take a closer look at the dates on the Metronome/Skill Hack/Foul Play rulings: they are from 2006, 2007, and 2011 respectively. Rules changing between different eras is a common occurrence (some examples are Fossil starts/giving up Prizes when KOed, or Rare Candy being usable on turn 1), so it’s not unthinkable that handling Energy discards with copy attacks was one such rule that was lost to the sands of time, perhaps because it didn’t come up that often in competitive games.

Another (circumstantial) piece of evidence comes from Togetic δ DF and Clefable DP’s Japanese wording. Note that DF and DP were consecutive main expansions in Japanese release order.

Togetic δ: 相手の場の「δ-デルタ種」のポケモンが持っているワザを1つ選び、そのワザのダメージや効果を、このワザのものとして使う。(選んだワザの効果などにしたがうことができないなら、このワザは失敗する。) (If you cannot follow the effects of the chosen move, this move will fail.)

Clefable: 相手のワザを1つ選び、そのワザのダメージや効果を、このワザのものとして使う。（自分のエネルギーに関係する効果にしたがえないなら、このワザは失敗。） (If you cannot follow the effects related to your energy, this move will fail.)

Below is a table showing the timeline of set releases and rule changes, in both English and Japanese:

Date	English Sets	English Rulings	Japanese Sets	Japanese Rulings
4 May 2006		Metronome succeeds if it copies Elemental Blast without proper Energy
29 Jun 2006			DF released	Togetic δ’s Delta Copy fails if you cannot follow effects of the chosen move
8 Nov 2006	DF released
30 Nov 2006			DP released	Clefable’s Metronome fails if you don’t follow effects related to your Energy
14 Feb 2007	PK released
2 Mar 2007			MT released
15 Mar 2007		3 rules related to Energy discards added to Compendium Skill Hack fails if it copies Hydro Wave or Mudslide without proper Energy
23 May 2007	DP released	Fossils give a Prize on KO
5 Jul 2007			PK released SW released	Fossils give a Prize on KO Shiftry ex’s Skill Hack fails if you don’t follow effects related to your Energy (same with Smeargle and Mew)
19 Jul 2007		Metronome fails if it copies Power Crush without proper Energy
22 Aug 2007	MT released
7 Nov 2007	SW released

Looking at the timeline, it would seem that the rule change for Energy discards and copy attacks happened at DP’s release in Japan, which is why Clefable DP has the new wording and Togetic δ doesn’t. The smoking gun is Shiftry ex’s place in the timeline. EX Power Keepers was released as the last set of the EX era in English, but after DP and MT in Japan. The ruling for Skill Hack in English is dated after DP’s Japan release. On PK’s Japan release, Skill Hack was printed (in Japanese) with the new, Clefable DP-like wording. At the same time, the Fossil cards in Japanese PK were printed with text stating they gave up a Prize when KOed (which was not the case for English PK).

All the seemingly contradictory rulings regarding Metronome or Skill Hack make sense as long as you treat 30 Nov 2006 (DP’s Japan release) as the Rubicon. Before 30 Nov, you can copy attacks without the required Energy to discard and still have them succeed. After 30 Nov, things get stricter and doing the same will have the attack fail.

My next post will be a summary of how to handle copy attacks and discarding Energy for different formats.

[dxdydzd]

Base-Neo

• If you have to discard Energy and are unable to, the attack fails. There is one exception to this: Dark Houndoom N4’s Dark Fire (the attack does not fail; you get the base damage only, but it’s better than nothing). Do not trust the wordings on the cards, English or Japanese, as several English cards were mistranslated and several Japanese cards were missing reminder text.
• If an attack tells you to discard all Energy, or discard all [type] Energy, you must discard at least one Energy, or it fails.
• If an attack discards Energy on a coin flip (e.g. Dark Flareon RO’s Playing with Fire), you can use it even if you don’t have the Energy that may be required (contrary to the English text). If you get the outcome that requires discarding and can’t discard, the attack does nothing (not even the base damage). If you get the outcome that doesn’t require discarding, the attack succeeds.
• Sabrina’s Abra G1 returns a [P] Energy to your hand. This is an effect, not a cost (contrary to the English text). That means it gets done after damage. If you don’t have a [P] Energy to return, the damage still goes through.
• For Base-Gym, discarding Energy is a cost and is done before flipping for Confusion.

EX

• If you have to discard Energy and are unable to, the attack succeeds unless the card specifically says otherwise (e.g. Slaking RS’s Critical Move). This holds regardless of how the discard is phrased: “discard a [type] Energy”, “discard all Energy”, “discard all [type] Energy”, or whether the discard happens on a coin flip.
• Blaziken RS does not have the “if you do” in its Japanese text, and should do 10 to the opponent’s entire Bench even if you can’t discard. The PK reprint has the right wording.
• If Shiftry ex PK uses Skill Hack to copy an attack that requires discarding Energy, that attack does not fail if you can’t discard the Energy, contrary to what the Compendium says. Note that this only holds in EX; in 2007, which is after DP, then it would fail.
• If a Pokémon copies Latias ex δ DF’s Power Crush and KOs it, but does not have 2 [R] Energy to discard, the attack still succeeds, contrary to what the Compendium says. Like Shiftry ex, this only holds in EX, not in 2007.
• A helpful pattern to notice is that attacks that say “discard a card” will fail if you cannot discard (even those that discard from hand, like Dark Marowak TR’s Hard Bone), whereas attacks that say “discard Energy” will not. However, some attacks had the word “card” unnecessarily added to “Energy” when translated from Japanese, e.g. Staryu DS’s Recover.

DP

• If you have to manipulate Energy attached to the attacking Pokémon in any way and are unable to, the attack fails. “Manipulation” includes: discarding, returning to hand (Absol G SV’s Doom News), putting in the Lost Zone (Arceus AR AR5’s Sky Spear), or moving to Benched Pokémon (Luxray DP’s Lightning Star).
• If you use Luxray DP’s Lightning Star without [L] Energy attached, but have no Benched Pokémon, it still does 80 damage.
• Charmeleon SW’s Flare Tail will fail, doing 0 damage, not even 50, if you flip heads but don’t have a [R] Energy to discard. (I take back what I said earlier now that I know the rules differ by format.)

BW-present

• If you have to manipulate Energy attached to the attacking Pokémon in any way and are unable to, the attack succeeds unless the card specifically states otherwise (e.g. Lugia-EX PLS’s Plasma Gale).

Universal Rule, applies to all formats

• If an attack says “You may (manipulate) Energy attached to this Pokémon. If you do, (effect)”, you only get the effect if you manipulated at least 1 Energy. If not, you only get the base damage (and effects, if any), but not the other effects or bonus damage for manipulating Energy.
• Note that this “manipulated at least 1 Energy” rule is only for attacks that are phrased “You may… If you do…”. If the attack starts with “Discard all…”, then it is handled differently based on format: in Base-Neo or DP it will fail if you can’t discard at least 1 Energy, in EX or BW-present it will succeed even if you can’t discard any Energy.

What about e-card and HS?
For e-card, the Japanese cards do not have the 「トラッシュできないとき、このワザのダメージはなくなる。」 reminder text on discard Energy attacks (e.g. Ember). However, Base-Neo cards do, so if you use a copy attack (e.g. Metronome) to copy a Base-Neo Ember, it would fail (you use Metronome, trace it to B-N!Ember, then B-N!Ember says it does nothing if you can’t discard). e-Card and EX Ember don’t have the clause, so what would happen in that case would be you use Metronome, trace it to e/EX!Ember, and it succeeds because neither Metronome nor e/EX!Ember say they fail if you can’t discard. Thus the expected behavior is that if the attack being copied is from Base-Neo, it would be “strict”, but if the attack being copied is from e-Card or EX, it would be “lenient”. Whether the Metronome is from Base-Neo or e-Card doesn’t matter.

(Side note: in e-Card, all discard Energy attacks were printed without the clause in Japanese. When they were translated to English, clauses were unnecessarily and inconsistently added to them. For some examples, compare Slugma SK, Raichu EX, and Cyndaquil EX with each other, then to their Japanese prints on pcg-search.com.)

HS has no attacks that copy other attacks, so it does not matter if you are playing just that block alone. However, in DP, the discard clause was handled differently from Base-Neo. Whereas Base-Neo placed the discard clause on Ember, DP placed the discard clause on Metronome instead (at least, it did in Japanese). BW did away with discard clauses on both Metronome and Ember. So if you were playing DP + HS, it would be strict (use DP!Metronome, try to copy Ember, but DP!Metronome says it fails if you can’t discard), but if you were playing HS + BW, it would be lenient (use BW!Foul Play, try to copy Ember, and it succeeds because neither BW!Foul Play nor Ember say they fail if you can’t discard). Setting HS as strict functionally achieves this: DP + HS is strict + strict, so strict; HS + BW is strict + lenient, but BW is newer, so it takes precedence; HS alone doesn’t matter since it has no copy attacks.

TL;DR
strict = fails if you can’t discard, lenient = succeeds if you can’t discard
Base-Neo: strict
e-Card: follows the era of the attack being copied. Base-Neo = strict, e-card = lenient, EX = lenient.
EX: lenient
DP: strict
HS: strict
BW-present: lenient

The reason e-Card isn’t simply “lenient” is that if you use an e-Card Metronome to copy a Base-Neo Ember, it will be strict.

[JasonKlaczynski]

The inconsistency with Clebable ex’s Metronome and Shiftry ex’s Skill Hack does seem weird, but it’s important to note that even though TPCi was a lot better than Wizards when it came to rulings, they still made mistakes, particularly in the early days. Clefable ex’s Metronome seems very clear that it should have to meet the discard requirements to perform attacks. I wonder if it wasn’t just simple human error when answering that question.

[dxdydzd]

Clefable ex’s Metronome says “You must still do anything else in order to use that attack”. The phrase “in order to” is very important, as this later ruling regarding Zoroark’s Foul Play demonstrates:

Q. If Zoroark uses “Foul Play” to copy Blastoise’s “Hydro Launcher” attack, do I have to be able to return 2 Water Energies to my hand in order to do the 100 damage?
A. No, the attack does not say “in order to” so you do as much of the attack text as you can. (Jun 9, 2011 PUI Rules Team)

Since Elemental Blast does not say “in order to” or “… or this attack does nothing”, it should not require discarding any Energy to get the damage under EX era rules.

My belief (which is the only way I can make sense out of all of these seemingly contradictory rulings) is that discarding Energy was “strict” in Base-Neo and DP (if you can’t discard, the attack fails), and “lenient” in EX/BW+ (the attack succeeds regardless, with rare exceptions that would be stated on the attack). This explains why Metronome copying Elemental Blast is OK (because it’s during EX), but Skill Hack copying Mudslide is not (because it’s during DP — even though Shiftry ex is from PK, the ruling was made after DP was released in Japan).

Japan chose to handle this new “strictness” rule by changing the reminder text on copy attacks. As mentioned above, Togetic δ (pre-DP) has the old text, and Clefable DP and Shiftry ex (both post-DP in Japan; Japan got PK after DP and MT) have the new text.

US chose to handle the new “strictness” rule by adding entries to the Compendium, while retaining the wording they had always been using on EX cards for DP cards. The added entries include the Shiftry ex Skill Hack and Latias ex δ Power Crush rulings (both these rulings are dated after DP’s Japan release), as well as these three “general gameplay” rules:

• If an attack has an energy discard requirement, a Pokémon copying that attack must also be able to do that discard in order to copy the attack. (Mar 15, 2007 PUI Rules Team)
• If an attack has an optional effect triggered by a discard, a Pokémon copying that attack must be able to do that discard in order to get the additional effect; if they cannot perform the optional discard, it still gets the base effect and damage. (Mar 15, 2007 PUI Rules Team)
• If a Pokémon attack copies another attack that says “discard all Energy”, then you must be able to discard at least one energy card of that type in order to use that effect or attack requirement. (Mar 15, 2007 PUI Rules Team)

Keep in mind the last ruling above did not survive till present day. In Standard, if an attack says “discard all Energy” or “discard all [L] Energy” and you are unable to discard, it still succeeds. Even as far back as BW, it was already retired (any translation errors are mine):

Q. I have a Zoroark with 2 Darkness Energy attached Active on my side, and my opponent has Raikou-EX Active on theirs. I can’t discard Lightning Energy, but can I use Volt Bolt with Foul Play?
A. Yes.

The interesting question for us retro players, then, would be “when did these rules get retired?” Was it at BW? HS? Some other point?

edit: JP managed to find this PokéGym thread confirming that a rule change for Energy discards did happen “some time” before 29 Mar 2007:

It turns out, that some time back in Japan, specific energy discards in attacks implicitly became requirements to perform the attack. This came to light in the discussion of Skill Hack v. Mudslide (and other attack copying effects like Skill Hack, e.g. Metronome). I say, “it turns out”, but confirming the change wasn’t quite so cut and dried as that phrase implies. A lot of checking had to be done, and then we had to figure out how to state it so that it didn’t become an over broad metarule and cancel other valid ruling guidelines like “do as much as you can”.

[dxdydzd]

For those who prefer tables to lists:

Attack Wording	Base-Neo, DP, HS (Strict)	EX, BW+ (Lenient)
“Discard a Energy”	Fails if you cannot discard	Succeeds even if you cannot discard
“Discard a Energy in order to use this attack” “Discard a Energy or this attack does nothing” “Discard a Energy. If you can’t, this attack does nothing”	Fails if you cannot discard	Fails if you cannot discard
“Flip a coin. If tails, discard a Energy” “Flip a coin. If heads, discard a Energy and (effect)”	Fails (you don’t even get the base damage) if you get the outcome that discards and you cannot discard, succeeds otherwise	Succeeds (with full damage and bonus effect) even if you cannot discard
“Discard all Energy”	Fails if you cannot discard at least 1 Energy, succeeds otherwise	Succeeds even if you cannot discard
“You may discard all/any number of/specific number of Energy. If you do, (effect)” “Discard as many Energy as you like”	Only performs the base damage if you cannot discard at least 1 Energy	Only performs the base damage if you cannot discard at least 1 Energy

may refer to a specific type of Energy, or not at all, the behavior would be the same either way.

Key phrases are in italics. Pay close attention to them to determine which category an attack falls under.

[dxdydzd]

Update:
It turns out I was mistaken, and Japan played with “can’t discard Energy = attack fails” even during EX. Thanks to coconutlacroix for finding this in a Japanese guidebook.

It seems the Clefable ex + Lugia ex ruling was incorrect, and English-speaking regions unknowingly played with the wrong rulings during that time.

So we have two uninterrupted time periods with different rules:

• From BLW onwards, if you can’t discard Energy, the attack succeeds anyway unless otherwise stated (e.g. Lugia-EX’s Plasma Gale).
• Before BLW, if you can’t discard Energy, the attack fails.

I have consolidated all the information on Metronome + Ember (and other types of Energy-moving attacks, like Energy Loop and Reflect Energy) in this document. flagrama is working on implementation.