Endbringer
Oath of the Gatewatch — rare
Creature — Eldrazi
Endbringer rulings:
2016-01-22: Endbringer untaps at the same time as the active player’s permanents. You can’t choose to not untap it at that time.
2016-01-22: If an effect states that Endbringer doesn’t untap during your untap step, that effect won’t apply during another player’s untap step.
2016-01-22: Activating the second activated ability after a creature has legally been declared as an attacker or blocker won’t change or undo that attack or block.