Cathars' Crusade

Whenever a creature enters the battlefield
under your control, put a +1/+1 counter on
each creature you control.
"Forth, and fear no darkness! Arise! Arise,
Riders of Theoden! Spears shall be shaken,
shields shall be splintered! A sword-day, a red
day, ere the sun rises! Ride now, ride now!"
— Theoden