Yeti

Trample, Yeti enters with a +50+50 counter on it. Whenever Yeti attacks, create 2 5/5 Yetimite tokens with 4 times damage to defenses that are attacking.
Level Up: Pay{10}{u}{u}{u}{u}{u}, put a +50+50 counter on Yeti. Yeti also creates 2 more Yetimites when attacking.