I know it's not a spell nor an abilitie, but let's get serious did you tryed the cooking pots?
You can create with thoses god gifted items some unkillables "walls".
As you would put a crate to block the path of a magister (just an exemple) the magister will just destroy the crate (this can take long with some of the 20k hp crate you can find early game). But cooking pots... have no hp si they will just "i am coming for you" you until you die... or until they die. They can dash you teleport them byby for 5 turn.
You can even puts cooking pots in the bottoms of stairs wich wont allow anyone to climb, creating a save place for evreone.
Because i speak about items and not spell i will mention another game breaker item for the undead. In fact it's more a bug but what a bug! One a the grotesque jar in the meister basement (in act2) will damage you on use (or diseased i dont remember). If you are undead it will heal you. Ok infinite potion will you tell me. No no no no no, the grotesque jar cost... 0AP so evry time you character play you can put him full life, that's quite... unfair.
For solutions, bringing the ia not to skip turn would be grat and instead moving crates/cooking pots away (or putting it in their pokets like a player would do?).
For the second one, because it's i think more a bug, maybe correct it ^^
On a more global level, i thing that making the IA of the ennemies better rather that just adding more armor and Rm and hp is a really better way for providing hight difficulty.
One simple improvment sould be the focus. Most of the time the ennemies will split the focus and end damaging 2 or 3 of your characters.
