Armasaur Guide 
Creature — Dinosaur
Vigilance (Attacking doesn't cause this creature to tap.) Whenever you attack with three or more creatures, put a +1/+1 counter on target creature you control.
Legality
standardLEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL