It took a couple weeks for our scheduled to realign, but we finally got Yagluth down. It was a freaking struggle, mostly because the fight ranged all over the plains biome that Yagluth was in, and we kept running afoul of adds - first some Lox that did way more damage to me than Yagluth himself did, then constant deathsquitoes and fulings, and at one point there was a 2-star fuling that nearly caused a TPW. At another point, Yagluth called down a meteor shower that destroyed our portal and the building it was housed in, and I had to keep him busy/drag him away while Emrys rebuilt the portal so that Keltsey could get back from being dead.
But in the end, we prevailed. Some lessons learned:
1) There's a reason why some people tunnel under Yagluth's altar before they summon him, so they can go down there to rest. This is a LONG fight and stamina is a real problem. It'd be real nice to be able to hide to take a breather without having to worry about adds.
2) Fire resist barley wine is absolutely essential
3) Health regen mead lasts only a few seconds but has a 2 minute reuse cooldown >_<
4) Yagluth's close range attacks are actually pretty weak. If you get right in his face, he doesn't use his laser-breath, and his own giant head blocks the meteor showers from hitting you. His Point Blank Area of Effect fireblast can be dodge-rolled with pretty easy timing, the invulnerability you get during the roll makes the first blast miss, and the lingering fire damage can be handled pretty easily by fire resist wine.
5) Bonemass power is still a pretty good idea. Yagluth doesn't do a lot of physical damage, but boy oh boy do the adds.
6) Even with frost arrows, the DPS of archery from range is way too low. His natural health regeneration will outpace it unless you have like six people, and it's easy to get so hyperfocused on shooting him you don't see incoming meteor showers. Best to get up in his face with melee instead.
7) The meteor showers are by far his most dangerous attack. When he raises his left fist, you gotta immediately stop whatever you are doing (unless you're right under his chin) and just run in a straight line. The meteors don't "lead" you but they have a large area of impact, and if you're standing still they will fall directly on you and demolish you. You might think you're safe if you're far away from him, but if you are anywhere within sight of him when he raises his fist, you're probably gonna get at least one meteor.