I have compiled a list of all known Wizards of the Coast printing errors and mistranslations. While most of these went uncorrected during their time, TCGOne has done a great job fixing these cards so that they can be played as the creators intended.
Dark Vileplume (Team Rocket)
Dark Vileplume’s Weakness should be Fire, not Fighting. Note that this error only exists on the non-holographic version of the card; the holographic version has the correct Weakness.
Grimer (Team Rocket)
Grimer’s Poison Gas should leave the Defending Pokémon Poisoned, not Asleep.
Blaine’s Charizard (Gym Challenge)
Blaine’s Charizard’s Roaring Flames should read as follows: Discard all Fire Energy cards not used to pay for this attack’s Energy cost. This attack does 20 more damage for each Energy card discarded this way. (This means a Blaine’s Charizard with 3 Fire Energy, for example, would discard two of these Energy cards and deal 60 damage.)
Rocket’s Minefield Gym (Gym Challenge)
Rocket’s Mineshould should place 2 damage counters on the Pokémon.
Metal Energy (Neo Genesis)
Metal Energy should only reduce damage received from attacks. This means Pokémon Powers like Dark Crobat’s Surprise Bite and Elekid’s Playful Punch should not have their damage reduced by a Pokémon with Metal Energy attached to them.
Slowking (Neo Genesis)
Slowking’s Mind Games should only work when Slowking is Active.
Unown D (Neo Discovery)
Unown D’s Darkness should only reduce damage done to your Pokémon with Unown in their name.
Unown M (Neo Discovery)
Unown M’s Metal should only reduce damage done to your Pokémon with Unown in their name.
Unown N (Neo Discovery)
Unown N’s Normal should only reduce damage done to your Pokémon with Unown in their name.
Feint Attack: Murkrow (Neo Genesis) & Umbreon (Neo Discovery)
Murkrow and Umbreon’s Feint Attack should not be affected by any affects on the Pokémon they are attacking, not just the Defending Pokémon, which, during the Wizards era, referred only to your opponent’s Active Pokémon.
Scizor (Neo Discovery)
Scizor’s Double Claw should read as follows: Flip 2 coins. This attack does 20 damage plus 20 more damage times the number of heads.
Dark Haunter (Neo Destiny)
Dark Haunter’s Call Back cannot be used if your opponent’s Bench is full. Your Bench size of course does not matter.
Mew (Wizards Promo #47)
Mew’s Psyshock should leave the Defending Pokémon Paralyzed, not Confused.