When Palace Jailer enters the battlefield, you become the monarch.
When Palace Jailer enters the battlefield, exile target creature an opponent controls until an opponent becomes the monarch. (That creature returns under its owner's control.)
8/23/2016 Palace Jailer’s two abilities can be put on the stack in either order. The last one to be put onto the stack will resolve first.
8/23/2016 If you’re not the monarch as the second ability resolves, the creature will be exiled until there’s a new monarch and that player is one of your opponents. The creature won’t immediately return just because an opponent is the monarch.
8/23/2016 Auras attached to the exiled creature will be put into their owners’ graveyards. Equipment attached to the exiled creature will become unattached and remain on the battlefield. Counters on the exiled creature will cease to exist.
8/23/2016 If a creature token is exiled, it ceases to exist. It won’t return to the battlefield.
8/23/2016 Palace Jailer leaving the battlefield won’t cause the exiled creature to return. The game will continue to watch for the next time an opponent becomes the monarch.
8/23/2016 The opponent that controlled the exiled card doesn’t have to be the same opponent that becomes the monarch in order to cause that card to return to the battlefield. Any opponent becoming the monarch will cause the card to return.
8/23/2016 The exiled creature will return to the battlefield just after the opponent becomes the monarch.
8/23/2016 In some unusual cases, Palace Jailer’s owner will leave the game while not being the monarch. In this case, nothing happens immediately, but the exiled creature will return to the battlefield the next time one of that player’s opponents becomes the monarch.
8/23/2016 The game starts with no monarch. Once an effect makes one player the monarch, the game will have exactly one monarch from that point forward.
8/23/2016 Abilities that trigger whenever you “become the monarch” trigger only if you aren’t already the monarch. For example, if you are already the monarch as Custodi Lich enters the battlefield, its last ability won’t trigger.
8/23/2016 If the triggered ability that causes the monarch to draw a card goes on the stack, and a different player becomes the monarch before that ability resolves, the first player will still draw the card.