Originally posted by fenlander:

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.

Just beat Yagluth a few days ago on my 2nd playthrough and I recommend against padded armor. makes you too slow.
My setup is ~:
1. Stamina, Health & Fire Resist potions.
2. high tier food (I think it was serpent stew, blood pudding and wolf skewer?)
3. Fenris armor for speed + Fenris hood for fire resistance OR padded helmet for higher armor level without speed drain.
4. Frostner + Silver sword (I think)

1+2 allowed me to regularly use the potions and stay aboe 100hp most of the time while tanking most fire damage "just like that."

And of course don't forget to clear the area beforehand.
Fight was no problem - even forgot to activate Bonemass's forsaken power (again) - but, to be fair, my character didn't start over so my stats are verrrrrry high (a few @100, most others between 50 and 70-80).