Andúril, Narsil Reforged
Legendary Artifact — Equipment
Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
Whenever equipped creature attacks, put a +1/+1 counter on each creature you control. If you have the city's blessing, put two +1/+1 counters on each creature you control instead.
Equip 
Jason Rainville
Rulings
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 you 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.
(wotc • 2023-11-03)
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 two, then cast Andúril, Narsil Reforged, you won't have the city's blessing.
(wotc • 2023-11-03)
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 your permanents. The city's blessing isn't a permanent itself and can't be removed by any effect.
(wotc • 2023-11-03)
If your tenth permanent enters the battlefield and then a permanent leaves the battlefield immediately afterwards (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.
(wotc • 2023-11-03)
A permanent is any object on the battlefield, including tokens and lands. Spells and emblems aren't permanents.
(wotc • 2023-11-03)
Rulings
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 you 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.
(wotc • 2023-11-03)
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 two, then cast Andúril, Narsil Reforged, you won't have the city's blessing.
(wotc • 2023-11-03)
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 your permanents. The city's blessing isn't a permanent itself and can't be removed by any effect.
(wotc • 2023-11-03)
If your tenth permanent enters the battlefield and then a permanent leaves the battlefield immediately afterwards (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.
(wotc • 2023-11-03)
A permanent is any object on the battlefield, including tokens and lands. Spells and emblems aren't permanents.
(wotc • 2023-11-03)