Contrary to Energy Flux, the final boss is a pain, though this is largely due to it dealing about 200 damage a hit, then actual difficulty. However, this is a two phase fight, so make sure to plan for it.
For every fight I strongly suggest using the gauntlets. Not only are they fast and deal decent damage, the charged punch attack has invincibility frames that make players immune to energy based attacks. From there, make sure you have five potions, the highest tier weapon/armor and both are fully upgraded.
The first phase is honestly the harder one and it’s all about avoiding sword attacks. The annoying thing is, if you touch the blade, even if it’s before or after an attack, you will take damage. This means the best way to play is always be in front of the boss and play defensively. If you don’t finish him quickly, the top part of it’s body will fly away and you’ll have to avoid rockets and its body. Sadly, I found dodging causes the rockets to lock on, so you basically want to just run around and hope he doesn’t run into you.
This is basically combo of Mutae and the Golem King. Basically all the boss can do is swing its arms in the middle, so stay on the side where it isn’t swinging and you won’t take damage. Eventually things will pop out of the ground, so keep moving until you think it’s safe and then proceed to attacking it. Outside of that, there will be an attack where it uses it’s arms to keep you in the middle. You should focus on dodging and staying alive and simply damage the boss after this attack. If you do this you should win without too many issues.