Steam Brawler

{x} can only be paid with Mana from Steam-powered Lands.
Steam Brawler enters the battlefield with X +1/+1 counters on it.
Whenever you cast a spell using mana from a Steam-powered Land, untap Steam Brawler and put a +1/+1 counter on it.
Remove a +1/+1 counter from Steam Brawler: Steam Brawler fights target creature.