If you wanted to do this, the same should apply to touch spells and bolts, I would think.

I feel like this would be really annoying. At the same time, it wouldn't add that much to gameplay. The strength of monsters that can pass through walls is that chokepoints are useless against them, but if you can't hit them in walls then you have to lure them into an open area. Sure you can get surrounded in open areas, but they could do that just as well in a corridor, because they can pass through walls.

Logically, I don't see a problem with hitting monsters while they're in the walls - if they don't stick out of the walls at all how can you even see them?

Bolts don't work on them. Touch spells are fairly close to ball spells IMHO (Burning Hands, Destroy Undead). Bless and Healing vs undead may be somewhat fishy I suppose.

If they can attack you, then there are going to be moments when a significant part of them is outside the wall (partially on your square, so to speak) and becomes hittable. Invincibility would just be unfair, and has potentially drastic consequences on the power level of these monsters. It's not like the ability to hit creatures inside walls is exploited at all at the moment. Players already prefer to lure them out in the open to fight them because they would have to dig out the walls to get at the loot otherwise.

If you absolutely have to change something to be happy, give creatures in walls a defense bonus. I don't see the necessity.

I think this is a good example of something that isn't broken and doesn't need fixing.

This would make Earth Temple pretty frightening if nothing else.

If this is considered, weopons 'of penetration' and phase weapons should stiil inflict damage.

Maybe simply add them some PV, as they are partly covered by wall?
Though it's still strange how ghost can be hit with a weapon at all.

Also, if they were entirely inside the wall and never showed any part of themselves, you wouldn't be able to tell they're there.

Silfir, this is the same telepathy that allows seeing monsters behind you.

No, that's the PC periodically taking quick glances over the shoulder, and having an image in his head of what he's seen. They're pretty good at it.

I agree with Grond, Silfir and SirTheta. I oppose this change.

My feeling is the same. There is no point making game realistic.