For me, again, just expressing a personal opinion, not a statement of fact, the worst bosses were the worst bosses thanks to either mechanics which I found gimmicky, or fights that seemed overly long and sluggish. Leaping to the head of the pack for my worst boss in the tier, then, is Amber Shaper Un'sok. His random transformation of players into vehicles with, as you'd expect in a vehicle, completely revamped abilities, is frustrating at best. In fact, I say it's random, but it isn't. Almost without exception, Un'sok has a remarkable ability to target the player least equipped to deal with a sudden transformation into Lord Ryolith. If the vehicle was something that could be targeted, or selected for a specific player, it would be fine, but that isn't the case. He is, therefore, number one on my worst boss list.