Sometimes during the fight with Kalah in the circus in Waukeen's Promenade, while I'm running around with haste on, casting magic missles at him, I will suddenly game-over. This can happen even with stoneskin active. Usually happens while playing solo sorcerer. It's not that big of a deal, just curious as to what it might be.

There's one thing you haven't mentioned. Is your character taking damage?

I still have stoneskin up when I "die" so I couldn't have taken any physical damage. Also Kalah didn't cast anything at me. The only thing I can think of is that maybe the werewolf illusions or shadows have a status effect linked to their melee attack that is bypassing stoneskin. I wish the game over screen would give some feedback as there are so many things that can happen to the PC that result in game over.

Not true. All 'on-hit' abilities ignore protections like Stoneskin and Mirror Image. That's why I asked if you were taking damage. So... is your character taking damage? There's only one status that results in game over, and that's if your character dies, whether in combat or scripted.

Game over can occur if the PC dies, is charmed, is dominated, is mazed, and probably some other things I'm forgetting about. As far as me taking damage, I'm at full hp, and then suddenly the screen goes greyish as it does when the PC dies. I don't hear any sounds like when I'm hit. That's really all the info I have. As far as the on-hit abilities, that's what I was saying, maybe the enemies have an on-hit ability that is bypassing stoneskin and causing the game-over.

I never use ranged weapons on a solo sorcerer, and I don't think thaco has anything to do with it, as stoneskin even deflects criticals.

According to their creature file, werewolf illusions only do 1D12 slashing

Hmm. Are you using the Enhanced Edition? See here.

I'm not using the enhanced edition. I guess I should have mentioned as well, I'm playing on Insane difficulty, although again, since I die with stoneskin still on, physical damage should have nothing to do with it.

Some of the dudes in Kalahs tent, at least in the EE, have ability drain I think. If your stats reach 0 that might kill you. Thats the shadows though not the werewolfs. I think.

As far as I know, the shadows only have str drain. Not sure if str reaching 0 results in death, I thought that only happened with int.

Any stat reaching zero results in death. For example:

In the unmodded game, stacking Contagion can cause death by stat loss. I actually used this to kill Imoen while still in Irenicus's dungeon. (Her Imoen's Belt prevents her from dying by ordinary means in order to allow her to leave, but this gets around that.)

Apparently, with at least one version of the fixpack, Harper's Call could be used to lower the stats of enemies, killing them that way. (The fixpack developers decided to implement the stat penalties mentioned in the spell description, but didn't think through the consequences, which is probably why the unmodded game doesn't give stat penalties with that particular spell.)

I believe there's a weapon that can permanently lower the attacker's Charaisma, which could drop it to zero. Of course, with the help of temporary Charisma bonuses, it is possible to underflow it and get permanent 25 Charisma. (The Ring of Human Influence helps here.)

That's probably what's happening to me then, my str being drained to 0. I guess I will start balancing out str/dex/con instead of dumping all my remaining points into just dex/con.

What level sorcerer are you?
I just tried a few times with a level 9 sorcerer with 10 strength & my 4 skins from stoneskin where always gone before I reached 4 strength
I died in one of them from 0 strength.