Mirror Entity is a special Creature — Shapeshifter card from Time Spiral Remastered (TSR), collector number 297. Current market price: $2.44 (foil $12.57), TCGplayer market prices via Scryfall.
Changeling (This card is every creature type.) {X}: Until end of turn, creatures you control have base power and toughness X/X and gain all creature types.