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.
Lazav is a mill/self-protecting Voltron threat: fill opponents' graveyards with creature cards, then have Lazav copy the biggest or most abusable one while keeping hexproof. You grind the early game with mill and value, then turn an opponent's best creature into your own hexproof commander to close out the game or assemble a combo.
Hexproof makes Lazav extremely hard to remove with targeted spot removal
Steals the best creatures opponents mill, turning their cards into your win conditions
Built-in card advantage engine when paired with self-mill and opponent mill
Flexible threat that can become combo pieces, beaters, or utility creatures on demand
Copy ability only triggers off creature cards hitting opponents' graveyards, so it can be inconsistent
Vulnerable to board wipes, edicts, and sacrifice effects that ignore hexproof
Mill can fuel opponents' graveyard strategies (reanimator, delve, dredge)
Lazav starts as a vanilla 1/1 with no evasion, so it needs support to actually deal damage
Heavy reliance on what opponents are playing to find good copy targets
Legendary Creature — Shapeshifter
