Experiment Twelve is a rare Creature — Elf Lizard Warrior card from Murders at Karlov Manor Commander (MKC), collector number 37. Current market price: $0.33, TCGplayer market prices via Scryfall.
Trample Whenever this creature or another creature you control is turned face up, put +1/+1 counters on that creature equal to its power. Disguise {4}{G} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)