Primeval Machine
This boss is really fun to fight except for one small, frustrating detail. The attacks themselves are very well telegraphed and it attacks frequently enough to where you are always moving. I find that all of the attacks are well made, maybe the rock throw can be a little ridiculous sometimes but whatever. The main gripe I have with this boss is the small platform you have to fight him on. It comes with many flaws that either allow you to cheese the boss entirely or just end up being a massive pain in the ass.
To start, the Parkour challenge is directly above where you fight the boss. This means that any class with range can just go up onto the platforms on the parkour and just sit there shooting the boss until it dies, and it has next to 0 way of fighting back. It can throw the rock occasionally but it's pathetically easy to dodge given its lengthy telegraph and how far away you are from it. I'm not exactly sure about how this can be fixed but it is definitely a very prevalent cheese to the boss that I think is kinda weird to have there.
Next, the platform you actually fight the boss on is too small. While you do have a fair amount of room to dodge its attacks normally, it's incredibly easy to just walk off the platform and get sent all the way back to the start of the room. It's very frustrating and feels needlessly small. The pillar from the TCC Statue also really gets in the way of the fight, I feel like it doesn't have to.
Overall Primeval Machine is an amazing mini boss, just the area you fight it in either allows for massive amounts of cheese or is just too small to feel good to fight him in unless you just face tank the attacks. If possible, I would recommend making the arena into more of a cage, so that you can't fall off the arena and also can't cheese the boss from the Parkour section above.