King of the Oathbreakers

• WWizards of the Coast2023-06-16
  Official Ruling
  Permanents phase back in during their controller's untap step, immediately before that player untaps their permanents. Creatures that phase in this way are able to attack and pay a cost of during that turn. If a permanent had counters on it when it phased out, it will have those counters when it phases back in.
• WWizards of the Coast2023-06-16
  Official Ruling
  A phased-out token will phase in at the beginning of its controller's untap step just like a nontoken permanent would.
• WWizards of the Coast2023-06-16
  Official Ruling
  If a spell an opponent controls targets multiple Spirits you control, King of the Oathbreakers's triggered ability will trigger once for each of those Spirits.
• WWizards of the Coast2023-06-16
  Official Ruling
  If King of the Oathbreakers phases in at the same time as one or more other Spirits you control, King of the Oathbreakers's last ability will trigger for each of them.
• WWizards of the Coast2023-06-16
  Official Ruling
  Any continuous effects with a "for as long as" duration, such as that of Rangers of Ithilien, ignore phased-out objects. If ignoring those objects causes the effect's conditions to no longer be met, the duration will expire.
• WWizards of the Coast2023-06-16
  Official Ruling
  An attacking or blocking creature that phases out is removed from combat.
• WWizards of the Coast2023-06-16
  Official Ruling
  Phasing out doesn't cause any "leaves the battlefield" abilities to trigger. Similarly, phasing in won't cause any "enters the battlefield" abilities to trigger.
• WWizards of the Coast2023-06-16
  Official Ruling
  As a creature is phased out, Auras and Equipment attached to it also phase out at the same time. Those Auras and Equipment will phase in at the same time that creature does, and they'll phase in still attached to that creature.
• WWizards of the Coast2023-06-16
  Official Ruling
  Choices made for permanents as they entered the battlefield are remembered even after they phase in.
• WWizards of the Coast2023-06-16
  Official Ruling
  Phased-out permanents are treated as though they don't exist. They can't be the target of spells or abilities, their static abilities have no effect on the game, their triggered abilities can't trigger, they can't attack or block, and so on.

Rulings via Scryfall