Leper can not only oneshot the final boss, he can also oneman it.

This took so many attempts it hurts just thinking about. To give an idea of the RNG at play here, if Leper gets afflicted at any point in this fight the run is over, there's no way for him to heal off the stress fast enough. It took around ~40 tries to get the perfect run, but it was worth it in the end.
I love the idea of Leper sacrificing himself and facing the eldritch horror on his own so others don't have to suffer. It's beautifully poetic.