Endbringer

Untap this creature during each other player's untap step.
{T}: This creature deals 1 damage to any target.
{C}, {T}: Target creature can't attack or block this turn.
{C}{C}, {T}: Draw a card.

Modern Horizons 3 Commander

Untap Endbringer during each other player's untap step.
{T}: Endbringer deals 1 damage to any target.
{C}, {T}: Target creature can't attack or block this turn.
{C}{C}, {T}: Draw a card.

Commander Masters

Jumpstart 2022

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Oath of the Gatewatch

Untap Endbringer during each other player's untap step.
{T}: Endbringer deals 1 damage to target creature or player.
{C}, {T}: Target creature can't attack or block this turn.
{C}{C}, {T}: Draw a card.

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.

Endbringer untaps at the same time as the active player's permanents. You can't choose to not untap it at that time.

If an effect states that Endbringer doesn't untap during your untap step, that effect won't apply during another player's untap step.