Klauth, Unrivaled Ancient
From Forgotten Realms Commander set
Klauth, Unrivaled Ancient
Legendary Creature — Dragon
4/4
Flying, haste
Whenever Klauth attacks, add X mana in any combination of colors, where X is the total power of attacking creatures. Spend this mana only to cast spells. Until end of turn, you don't lose this mana as steps and phases end.