If you got a mountain range and a meadows nearby; set up a wolf breeding farm.

Set up a small base where you can grow some food and flax, but also where you got a portal.
Mine out a large enough area for the wolves to live in near it, make sure you're able to leave that area using stairs.

Next, head to the meadows and try to tame several boar; one at a time.
When you tamed one, lead (read: push) it back to your base and close to the pit in a seperate pen. Just make sure you cover the pen with a roof to avoid the boars being killed.

Next head to the mountain and lure the wolves into the pit.
Would even be better if you got the "Hunt-event", but there's more risk with that one.

Start feeding your boars carrots or any other vegetable you can grow at a meadows base so they get off spring. Once you got a few boars, kill the oldest ones - or the off spring - and feed the meat to the wolves.
Once the wolves are tame, keep feeding them to get more wolves.

Eventually when you have around 30-50 wolves, create a slope and order your wolves to follow you.
Head out to the altar, do the sacrifice and let your wolves attack Yagluth.
While most of your wolves may die, the damage they do and the fact Yagluth is concentrating on them gives you the time to move in and hit him as well. With the right weapons - which are already mentioned above - the fight will be short and in your favour.

Thorin :)

Hello, my method: dig a deep and wide enough trench around the altar. Within range of your bow, use the hoe to create a wall behind which you can hide and place the transmitter. From the moat, lead a short channel in your direction. Out of 4 actions, Yagluth stayed 2 times in the channel and 2 times on the sacrifice, and if I didn't significantly reveal myself from behind the wall, he just stood and stared stupidly. I think I used about 300 ice arrows, silver, iron work. It takes longer than it is after, you need to get a second bow or repair it. Quite calmly, it can be regenerated at the base using a transmitter.
I used a translator, so excuse any mistakes.

i killed yagluth using the fenris armor for the speed bonus as well as the fire resistance u get from it. and i used frostner mainly but when i got low enough i ran away and fired frost arrows and kept my distance . good tip.... clear the area around the boss area for goblins and loxes and bugs. i died two times but since i had a portal closeby it was easy to get back and get my things. use the stone pillars to hide from the fire laser and the meteors.

Please Help.

Never solved the problem of trying to take Yagluth out on open ground. Both times, I've built earthworks, pulled him in close and killed him with silver arrows (he's undead). Requires preparation, including 600+ silver arrows (probably pierce resistant) and multiple bows (unless you provide for fast repairs, since he's going to be healing rapidly while you're gone).

Fire resistance potions, healing and stamina potions....I just hacked it to death with a blackmetal sword. Hide behind the stone pillars at the alter to get your stamina back when you can. I thought Yagluth was easier than Bonemass actually. I would just watch some youtube videos on it, someone has to have recorded a fight with Yag by now?

Yagluth is the first boss that you have to treat like a real boss fight. First of all, you need Frostner or a blackmetal sword and blackmetal shield, padded armor (all Level 4). Silver arrows work ok, but there's not much time to shoot. Serpent Stew, Lox Pie, and Bread for food. Have a Fire resist mead up at ALL TIMES. He does 3 attacks.

Flaming Meteors from the sky: Run away from him diagonally and hide under one of the altar fingers if you need to.

Fire Breath laser attack: Run closer to him diagonally, in the direction his breath attack is rotating towards.

Fist Slam: This attack produces a blue PBAE effect. you can just block or parry it. Be in melee range and preferably behind him when this happens (remember you just ran back closer to him). After blocking, unload damage on him with up to 3 3-hit combos. Be ready to run diagonally away when he calls back the Flaming Meteors.

Use health and stamina potions as needed.

Repeat.

Build a raised plateau in view of his altar. About 8 raises with the hoe per section. Make the plateau big enough to accommodate a portal back to your base.
Next, build frost arrows. They do substantially more damage than all other arrows, silver included. About 300 arrows should be fine.
Summon the boss, and immediately run up the plateau you constructed. Yagluth, will be unable to path to you and will literally just stand there. Rain arrows on him until he is defeated.

Its OK to run away to heal if you get hit. Keep your health topped off by melee a bit, then when you take 25% or more damage get out, behind the alter rocks or whatever, heal for a min, try again. It can be a long fight.