- First of all, I've heard a few people ask about this in the comments. Maybe you could add the red soul just like the other souls?

- Another popular suggestion, it would be cool if you added monster souls/monsters being able to absorb souls. Maybe monsters could gain hp/strength if they absorbed human souls?

- Why not add some unused characters like Doge and RG 03/04?

- I just thought of this one as I was typing this, what if you added the Omega Flowey attacks such as the teeth thing, the flies, and the flowey bombs?

- Lastly, what if you added abilities to the souls as alternative versions in the spawn menu? Some examples of this are making a alt version of the yellow soul that shoots, a dark blue soul that's not weightless, and a green soul that has a shield.

That's all from me, have a great day/night y'all.