Endbringer
Creature — Eldrazi
Untap this creature during each other player's untap step.
: This creature deals 1 damage to any target.
: Target creature can't attack or block this turn.
: Draw a card.
Adam Paquette
Magic Online Promos (PRM)
• #59667Rulings
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.
(wotc • 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.
(wotc • 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.
(wotc • 2016-01-22)
Rulings
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.
(wotc • 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.
(wotc • 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.
(wotc • 2016-01-22)