This might not appeal to everyone but for me the more bosses the better
- Grotesque Guardians
- Sarachnis (just an idea example, add something like a cudgel handle that adds more attack bonus or something)
- Zalcano
- Allow pets to roam in POH, maybe max it too 10 pets at a time you can select?
- Darkmeyer Agility course, it's different to just running a rooftop and can recolor graceful to black.
I know the first 3 bosses don't offer a lot in terms of drops but maybe you could add unique drops to them to make people want to do them even more.