Killer Cosplay is a mythic Artifact — Equipment card from Unfinity (UNF), collector number 145. Current market price: $0.19 (foil $0.24), TCGplayer market prices via Scryfall.
Whenever this Equipment becomes attached to a creature, choose a creature card name with an identical mana cost. That creature becomes a copy of the card with the chosen name until this Equipment becomes unattached from it. Equip {3}