Kefnet, Avenger of Amonkhet

Flying, vigilance, indestructible
Kefnet, Avenger of Amonkhet can't attack unless your opponent is playing a red, black, or blue deck.
{4}{u}: Destroy target noncreature, nonland permanent. Lands you control gain "If this card would become tapped, add {u} to your mana pool." until end of turn.