Mega Gengar

Flash
{p/b}{p/b} Exile Mega Gengar, return it to the battlefield at the beginning of the end step.
{p/b} Mega Gengar cannot be blocked until the end of the turn.
Whenever Mega Gengar is exiled, exile target creature.
Whenever Mega Gengar attacks, put target creature in exile into its owner's graveyard.
When Mega Gengar dies, exile Mega Gengar