The only time I killed Yag it was solo. I had max tier padded, fire resist, med heals, and stamina potions. I used a max level frostner. I spawned him in , popped the bonemass special, and face tanked him until he gave up the ghost, it was quick, I don't think I had enough time to pop more than one or two stamina/heal.

*edit : I went first thing in the morning. (through portal, with rested bonus, cleared the area first)