Vesuvan Doppelganger is a rare Creature — Shapeshifter card from Revised Edition (3ED), collector number 88. Current market price: $18.14, TCGplayer market prices via Scryfall.
You may have this creature enter as a copy of any creature on the battlefield, except it doesn't copy that creature's color and it has "At the beginning of your upkeep, you may have this creature become a copy of target creature, except it doesn't copy that creature's color and it has this ability."