Theto, Diviner of Truth

Flying, indestructible
Creatures you control have "{t}: Add {u}{r}. Use this mana only to cast instant or sorcery spells. When this mana is used to cast an instant or sorcery spell this turn, this creature deals 2 damage to each opponent."
Theto can't attack or block unless there are five or more instant and/or sorcery cards in your graveyard.