Keen-Eyed Raven 

Creature — Bird
Flying (This creature can't be blocked except by creatures with flying or reach.) When this creature enters, put a +1/+1 counter on another target creature you control.
Legality
standardNOT LEGALpioneerNOT LEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL