your questions regarding the game rules (improving the interpretation).

It is allowed to enter the Treasury using wings or the Fly spell, but only through generated passages, and it is necessary to kill the guard or one of the guards of that passage. It is forbidden to fly over mountains.
The Destruction Domain spell is allowed to be used in one of the cells, as close as possible to the Guardian of the Objective that the player is going to attack. And can you provide a link to a picture from that game where it is not allowed?
If you start with this, would that be okay?