Phantom, Bloodshot Execution

When Phantom, Bloodshot Execution enters the battlefield, destroy target creature, then draw X
cards, where X is equal to the number of creature
cards in the destroyed creature's controller's graveyard.
{t}: Target player loses X life, where X is equal to
the number of creature cards in that player's graveyard.
At the beginning of your end step, if an opponent
has one or less creatures in their graveyard,
transform Phantom, Bloodshot Execution.