Yagluth used to be tankable but now you do actually have to move around a abit since they upped his fire damage, even with fire resist theres a limit to how much is tankable. He should cycle through either aoe and metoer if your close enough to him, if you get far away enough he'll do beam attack.

A few different strategies can be used but mainly you have to keep an eye out for his openings, which he has but you don't usually get heaps of hits maybe 2 full combos.

I'll post a video, it shows yag getting beatdown without any tanking allowed