If you are fighting Moder and are properly equipped you should have serpent stew, cooked lox meat and sausages. Fully upgraded Wolf / Silver gear.

First you should use Bonemass power to reduce damage taken. Since you are two people you can have one person do one and when that runs out <or about to> the other person can trigger it. This will give you 10 mins of damage reduction. Use frost potion on top of wolf gear, it may take some of the edge off the frost attacks.

Use poison arrows with drauger bow <upgraded> Moder is immune to the cold damage from frost arrows. Rush in when it lands and melee. Silver sword works well.

Dig around the Moder spawner. You can run around it an use it for cover.