Mausoleum Harpy

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.

If another creature you control is dealt lethal damage at the same time that Mausoleum Harpy is dealt lethal damage, Mausoleum Harpy won’t be saved by the +1/+1 counter that would have been put on it.

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.