Mercenary Cavalry

Haste, Trample
Mercenary {2} (At the beginning of each player's
upkeep, that player may pay {2}. If they do, they
gain control of this creature, then untap it. It can't
be sacrificed.)
"The cavalry hit the enemy formation from the side,
and as quickly as they came they routed the enemy."
-Ivan, Kreggan Sergant.