I am preparing his altar now for when I summon him in my solo play through. I have raised palisades using earthen works so they can't be destroyed, and thankfully the altar is right next to the sea. So I made a trench in the water to keep me wet when attacking so it puts the flames out.

I have a portal under a rock that links back to my home base, just in case I die. Currently I am eyeing up the Lox near his altar which I am going to tame and bring to the fight. Also I need to breed them for meat.

Got a fully upgraded Frostner, padded armour and fire brandy. I find preparation is key to defeating the bosses in this game after Eykthir. Arrange the battlefield to suit your play style and tactics.