The cursor doesn't show up on windows version on my pc. I couldn't beat the last boss.
For the parkour section it seems the second jump starts after the player starts going downwards, it ends up making the timing flawed, and the double jump can seem a little unresponsive. It would also be nice to have a indicator as to when I can dash. I think the double jump should be timing based and not based on your y velocity.
The undertale section it seems the entire heart is a hitbox, it caught me of gaurd as in normal undertale the hitbox is smaller than the heart considerably so. The blue soul is too floaty for the final precise jumps.
The final boss seems fine if I had my cursor.
The game is pretty good other than these issues I had, I think a bit more polish can make this a master piece. It also has a decent amount of content, which is nice to experience and I quite like the way the story is told.