Ascend

Ascend is a keyword ability that makes you get the city's blessing for the rest of the game if you achieve to control 10 or more permanents. It was introduced in Rivals of Ixalan, and is primary in white, blue, and black.

Description
Ascend unlocks different bonuses on different cards if you have the city's blessing. Ascend always looks at the current game state, not the past. If ascend is on a permanent, it constantly checks to see whether you control ten or more permanents. The moment you do, you get the city's blessing. When Ascend appears on instants and sorceries, it checks if you control ten or more permanents only once, as the spell resolves.

Ascend doesn't use the stack and can't be responded to, but note this only is relevant if the land is the tenth permanent, as the only special action that adds a permanent. The permanent with ascend has to be under your control to check. Spells with ascend also do other things. Those instructions appear after the ascend ability, so they'll happen after the check.

Once you have the city's blessing, you keep it for the rest of the game. Multiple players can all have the city's blessing at the same time.

Rulings

 * Once you have the city's blessing, you have it for the rest of the game, even if you lose control of some or all of your permanents. The city's blessing isn't a permanent itself and can't be removed by any effect.
 * A permanent is any object on the battlefield, including tokens and lands. Spells and emblems aren't permanents.
 * If you cast a spell with ascend, you don't get the city's blessing until it resolves. Players may respond to that spell by trying to change whether you get the city's blessing.
 * Ascend on a permanent isn't a triggered ability and doesn't use the stack. Players can respond to a spell that will give you your tenth permanent, but they can't respond to getting the city's blessing once you control that tenth permanent. This means that if your tenth permanent is a land you play, players can't respond before you get the city's blessing.
 * If you control ten permanents but don't control a permanent or resolving spell with ascend, you don't get the city's blessing. For example, if you control ten permanents, lose control of one, then cast Golden Demise, you won't have the city's blessing and the spell will affect creatures you control.
 * If your tenth permanent enters the battlefield and then a permanent leaves the battlefield immediately afterward (most likely due to the "Legend Rule" or due to being a creature with 0 toughness), you get the city's blessing before it leaves the battlefield.
 * Some cards have triggered abilities with an intervening "if" clause that checks whether you have the city's blessing. These are worded "[Trigger condition], if you have the city's blessing, [effect]." You must already have the city's blessing in order for these abilities to trigger; otherwise they do nothing. In other words, there's no way to have the ability trigger if you don't have the city's blessing, even if you intend to get it in response to the triggered ability.
 * Some cards have triggered abilities that check if you have the city's blessing, but don't use an intervening "if" clause. These abilities trigger regardless of whether you have the city's blessing and check whether you do only as they resolve.
 * Some cards get power, toughness, and/or abilities once you have the city's blessing. If another card has an ability that triggers when creatures with certain characteristics enter the battlefield (such as Mentor of the Meek or Elemental Bond do), use the entering permanent's characteristics after you have the city's blessing to determine whether those abilities trigger. This is true even if the entering permanent is your tenth permanent.