Mona Lisa, Ever Adaptable is a rare Legendary Creature — Lizard Mutant card from Teenage Mutant Ninja Turtles Eternal (TMC), collector number 126. Current market price: $3.27, TCGplayer market prices via Scryfall.
Whenever a player casts a creature spell, you create a Mutagen token. (It's an artifact with "{1}, {T}, Sacrifice this token: Put a +1/+1 counter on target creature. Activate only as a sorcery.")