There's a part once you make it to the very top of the stairs outside of the building and there's just countless yellow bar minotaurs, hobgoblins, and goblins. You have to kill the Y shaped thing (can't remember its name) to keep them from spawning which is tough because of all the bastards shooting at you and the hobgoblins behind it sniping you. That part is pretty bad but after that, it's an easy run to the actual boss. The Undying Mind is basically the Nexus covered in mold with 3 orange vertical rectangle shields and spawn adds based on how much health it has. The splash damage radius is ridiculous and can sometimes hit you while you're hiding.