Am at the door to where Desther is in the bottom of helms hold.How do you beat this guy!!nothing hurts him and he has lots of help.Plus you can't teleport out to heal.I keep losing Tomi and get deseased etc!!??Any help??Thanks

Kill the ritual creatures that are around him. Once they're all dead, he become vulnerable.

you dont even have to kill all of them, just enough to make a break in the magic lines surrounding him, then he runs out at you