Darkness Energy (DP 129). Darkness Energy (RR 99). If you add basic Dark energy before special dark it won't allow you to add anymore. It works properly if added the other way around though
------------------Begin Game Log------------------
The game is about to start
Type: QuickPlay
Format: 2009 (DP–RR)
Battle begins between chaosofslayer and TheWombat!
TheWombat will take additional mulligan(s) after chaosofslayer sets up to play.
Mulligan phase: TheWombat took 1 additional mulligans
chaosofslayer drew 1 extra cards.
Coin flip [Opening Flip]: TAILS
TheWombat will start
Game setup complete
Between turns
Turn 1 begins
TheWombat drew 1 card
Put Vulpix onto bench.
Between turns
Turn 2 begins
chaosofslayer drew 1 card