keeps kicking my party's asses. how do I beat it?

I recommend one of your party members has a adamantine weapon and avoid casting fire spells (or using fire elemental pets) since they heal them.
I usually try to get the ice aoe spell in place as early as possible (they will take damage per step). Once it reaches the adamantine wielder put a hold spell or web in place. You can have a second warrior nearby even without the ability to damage it might split the damage taken.

Thanks! I will try this

fire pets are nice at other times thou because you can heal them with fireballs ;)