| Grailknight |
Ice Tomb is your friend here. It is open to debate if Retribution works on on undead. It targets will but does not have language stating saying it is mind-affecting so you should discuss with GM beforehand.
As far as spells go, Undeath Ward will give you some protection but Summon Monster 5/6 are your only real offensive choices. Snowball and Intensified Snowball saw me through some rough patches also.
You can always fallback on buffing the party with Fortune
| Decimus Drake |
Retribution isn't a mind affecting hex so it'll work on undead; that it allows a will save doesn't make any difference, cure spells work on undead and they allow will saves too. Similarly Misfortune allows a will save but isn't mind affecting.
I'm not sure if it's worth it but the Healing and Major Healing hexes would work on undead; you could use the Barrow Haze spell to give you range. No idea if it's any good but the level 5 Lesser Summon Psychopomp spell allows you to summon 1d3 esobok which have an attack that can instantly destroy unintelligent undead and stun intelligent undead.