Valefor, Besaid Aeon

Flying, aeon (When Valefor enters the battlefield, tap an untapped summoner creature you control. You may choose not to untap it during your untap step. When it becomes untapped or you don't control a summoner tapped with Valefor, shuffle Valefor into its owners library.)
{t}: Tap target creature. It doesn't untap during
its controller's untap step.
{5}, {t}: Valefor deals 3 damage to each creature target opponent controls.