Okay then, current plan iteration would involve Bastion flying in at night (Via potion of fly) while carrying Deanna and Albrecht, and landing on top of the tower. We'd be asking Deanna to use that position to do her thing. Use fireballs and whatever other tricks she has to rapidly whittle down their numbers from above.
Does she have particular objections/concerns to this approach?
Edited: daishain on 14th Apr, 2017 - 9:54pm
Basically intend to advance on foot along whatever route seems least likely for shadowy movements to be spotted, probably from the east or west of the fort near the ravine. About 50 paces prior to reaching the extent of what we expect their visual range to be, popping the fly potion, flying up to and along the cliff face at a few hundred feet up, and then dropping down to the tower from directly overhead.
So time of flight would be however long it takes to complete that route while moving 40' per round. If we're talking ~300 feet up and the same in horizontal distance (So a little under 900' total), it'l be about a minute and a half.
If casting her spell just prior to contact is particularly beneficial, we should be able to pause above the fort and use the cliff face to stabilize her (Good maneuverability as granted by the fly spell can be used to hover.).
Main issue with this is as follows. There is no covered approach to the strong hold. Imagine that a mountain split with a good 3,000 feet of it sheering off into a cliff. The rocks and other debris cascaded downward leaving a ruble strewn area of about 1/2 mile with the stronghold situated in the middle. The ravine was formed during this. When you get close to it you will see it is about 60 feet deep. The causeway to the strong hold was made with the stones that were from the cascade. The rock has been also used in the building of the strong hold and some more stone has been been harvested into the mountain side where it now have areas that you can see going into the mountain what is in there you can not see.
We were at least partially aware of the no cover on approach. This is why we were wanting to do this the night of the new moon, so there's as little light as possible other than whatever lights they have at the fort itself. Even Darkvision only helps so much on a moonless night.