Endbringer

five generic mana one colorless mana Creature — EldraziPower and toughness5/5

Untap this creature during each other player's untap step.

tap this permanent : This creature deals 1 damage to any target.

one colorless mana , tap this permanent : Target creature can't attack or block this turn.

one colorless mana , tap this permanent : Draw a card.

Showing Oath of the Gatewatch#3

Price

0.33 $

Foil 1.77 $

29 printings · up to 0.55 $

Daily estimate from Scryfall, not a shop quote.

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.