Lazav, Dimir Mastermind is a mythic Legendary Creature — Shapeshifter card from GRN Guild Kit (GK1), collector number 16. Current market price: $0.70, TCGplayer market prices via Scryfall.
Hexproof Whenever a creature card is put into an opponent's graveyard from anywhere, you may have Lazav become a copy of that card, except its name is Lazav, Dimir Mastermind, it's legendary in addition to its other types, and it has hexproof and this ability.