Sanguinius, Father of Blood

Flying, Menace, Double Strike

Black Rage—(at the beginning of your combat, all creatures you control gain +X/+X until end of turn, where X is equal to Sanguinius’s Power)
Whenever a creature enters the battlefield, they gain a Blood Counter. If a creature leaves the battlefield with a blood counter, Sanguinius gains two +1/+1.
If Sanguinius leaves the battlefield, all creatures gain +X/+X counters and gain menace and double strike, where X is Sanguinius’s Power.