I killed Moder, the 4th boss in Valheim. This is a grueling experience all around.
First off, just summoning him is quite the chore. You need 3 dragon eggs which weigh 200 each, so even if you have the girdle that increases your carrying capacity from 300 to 450, you can't carry all 3 eggs by yourself at once. His summoning altar is quite far from my main base and it was quite the journey on my ship, especially with the wind not cooperating and me having to tack yo sail against it. I built a summoning portal near the altar once I reached it. Unfortunately, you can't take dragon eggs through a portal (still worth building it, though), so I had to make the last leg of the trip from shore and up the mountain side multiple times. I felt like freakin' Odysseus after all that.
After dropping the eggs near the altar, I ported back home, rested, got all my food and supplies ready, then ported back and performed the summoning ritual.
Moder has ice attacks, so frost resistance is a must. My wolf armor and lox cape all have frost resistance, but I drank ftost resistance mead for good measure and used Bonemass' power for physical resistance. I mainly used my Draugr Fang bow with poison arrows. He's a massive bullet sponge, so this took FOREVER, but I was never in critical danger so long as I didn't try to melee him when he landed. His bite attack does stoopid damage.