The Alien Grays

Hidden Agenda (This Conspiracy starts the game face down in your command zone.)
Once a creature with flying enters the battlefield,
turn The Alien Grays face up. For the rest of the
game, whenever a creature deals combat damage
to you, you may take control of that creature,
whenever a creature blocks a creature you control,
you may take control of the blocker, and whenever
a creature you control blocks, the attacking creature's
controller takes control of the blocker.