Gigantoplasm is a rare Creature — Shapeshifter card from Ravnica Remastered (RVR), collector number 450. Current market price: $0.67 (foil $0.62), TCGplayer market prices via Scryfall.
You may have this creature enter as a copy of any creature on the battlefield, except it has "{X}: This creature has base power and toughness X/X."