ToME: the Tales of Maj'Eyal

1. Aether Beam can be put on wall.
?nd it inflicts damage on both sides of the wall. This is a cheat. For example, I easily defeated the Rhaloren Inquisitor (Rhaloren Camp) with just a few Aether Beams, placed on the wall of her little room. She helplessly tossed between two closed doors, and eventually died. Arcane Eye helped oversee this process.

Monsters in Dungeon Vaults, seen through the Arcane Eye, is also successfully attacked via wall-placed Aether Beam. Of course, humanoids have the sense to run outside and chase the hero.

2. Zero-damage from Aether Beam and from Aether Breach.
But in the Old Forest, a group of snakes get zero damage from Aether Beam and from Aether Breach, as long as you do not see them first time through the eyes of the hero, and not through the Arcane Eye.

Here on the forum there was mention that the zero damage from Aethers is related with the sleeping status on targets.
I know too little about the spells noise and about hero move noise. But note: in the Old Forest can be cleared center area with snakes (via Breach), but snakes at the edges, which you do not see - will continue to receive zero damage for a several casts.

Sorry for the difficulties of translation. In other words - is suppressed tactics. Unable to quietly sneak up and put Aether the corner from afar, seeing the targets only through the Arcane Eye.

In the case 2, you can right-clicked the monster and look its status and see 'In Vault' statement. In this case, it cannot be harmed before you awake them via introducing them into your LOS.

This has to deal with monster pits (the snake pit you mentioned, for instance) being deemed 'vaults' for reasons of the 'in vault' status, which keeps monsters from wandering, to prevent level slowdown.

You will notice the same thing in some of the enclosed rooms in Dreadfell (Korpul does it to, I think?), and any large vault. If you toss a spell into the vault, and the enemy hasn't been seen yet, by you, it's immune to the damage, in the same way.

I had something similar happen to an oozemancer through having more than 10 light radius. The Room of Death is large enough that the far corner wyrms had the In Vault status while I stood in the doorway immutable while I tried to aggro them one at a time with the poison spores attack.

In Vault should probably break on damage even if LOS tricks are fixed.