Chapter 7 and 8

The last 2 chapters are very hard.

The final stand (chapter 7)
Gaster is a very powerful boss. You fight him 3 times.

One in the minions of sentie.

one in chapter 4

one in chapter 7

The only way to win is get him off the area.

Heres a photo. (see end)

The Genocide End (chapter 8)
Includes a very hard boss named Chara-- yes you might know her from undertale cuz why not