Karlov Watchdog 

Creature — Dog
Vigilance Permanents your opponents control can't be turned face up during your turn. Whenever you attack with three or more creatures, creatures you control get +1/+1 until end of turn.
Legality
standardLEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL