Themberchaud is a rare Legendary Creature — Dragon card from Universes Within (SLX), collector number 28. Current market price: $20.36, TCGplayer market prices via Scryfall.
Trample When Themberchaud enters, he deals X damage to each other creature without flying and each player, where X is the number of Mountains you control. You may exert Themberchaud as he attacks. When you do, he gains flying until end of turn. (An exerted creature won't untap during your next untap step.)