Renegade Doppelganger is a rare Creature — Shapeshifter card from Rise of the Eldrazi (ROE), collector number 84. Current market price: $0.55 (foil $1.20), TCGplayer market prices via Scryfall.
Whenever another creature you control enters, you may have this creature become a copy of that creature until end of turn. (If it does, it loses this ability for the rest of the turn.)