I beat Yag for the first time not too long ago. Frostner, 2 health+1 stam food, all available potions. I ended the fight with about 3 minutes of fire resistance left and I never needed bonemass. he doesn't call adds as far as I know, but you need to clean the area before the fight. I did get a skeeter during the fight even still tho. some poor folks get hunted during the Yag fight so just remember it can always be worse in Valheim too