This boss requires luck to win, plain and simple (or play blood DK where you can just never die)
You can watch a youtube guide if you want, it won’t help you. Those spawns will just land anywhere for no reason at all sometimes, even if you try to position him precisely.
Stand him against the wall? You’ll still get the spawns spread out randomly all over 50% of the time; slightly away from the wall? Same again… It does not matter where you position him, they will sometimes just land all over the place… Yes, even if you leave the delve and try again.
Basically, the factor that spoils this boss is that sufficient bombs and time were not provided to deal with chaotic spawns. This means that you can fail for a reason outside of your control.
So, what limiting factor do the bad spawn locations amount to?
Wasted time.
If they’re all standing together on the correct terrain (where it won’t randomly block your bomb kick) you save a massive amount of time. When you have them spread in three different locations or more, you end up in a compounding snowball that is basically impossible to escape from.
So… Spawns randomly appear all over the place; you run around and deal with them, but by the time they’re dealt with, guess what? He is sending in more goons, but because his positioning is bad due to you having to deal with the spread out goons, you will be dropped right back in the same position that you just dealt with (even with good positioning, it’ll still just send them all over sometimes).
So now you’re back to square one… And on and on it goes. Something that isn’t your fault, that you cannot control, is the reason you may fail the underpin fight.
This is TERRIBLE game design. This is not true difficulty or challenge, because it is a factor completely outside of our control.
You cannot force the enemies to spawn in reasonable locations, and the boss fight has not been designed for you to have time to deal with enemies landing in three or more random locations.
Intelligent and fair design would mean giving your players time to deal with the factor they can’t control; otherwise you have something that is inherently unfair. People do not like unfairness, which is why people enmasse do not like this bossfight.
That you would think to put a limited time mount behind something like this just adds insult to injury. You may as well just have people roll a dice for who gets the mount.
I actually find the fight so disrespectful of the players; that they would shovel this slop to people as if it is a genuine challenge. This is faux difficulty.
Real difficulty means the player made a mistake, and that is why they failed. Fake difficulty is when the game can initiate a loss state without the player having influence over it.
Worse still is that they don’t consider how much worse it is for classes with limited range. Like, my god… Rogues have it so bad here it is ridiculous. Ranged don’t have to worry if the boss is in a bomb radius, so they have a lower mental stack. Meanwhile, if you’re melee, you have to also make sure the boss is away from any bombs before he shields. Another significant layer of difficulty just thrown on top without consideration.
This boss is an embarrassment, and honestly, they need to either remove the time limit on this achievement, or fix the boss and extend the time needed to acquire it. You cannot put limited rewards behind a boss that has unfair difficulty baked into it, and not expect people to feel resentful towards the people who made it.