Fun game, gave me some Binding of Isaac vibes mixed with Luigi's Mansion (because of the ghosts I guess).
The main mechanic is interesting, forcing the playing to think about the best order to kill the enemies. Taking it up a notch, you could "fusion" souls for better or worse effects. Like, Dizzy + Paralysis => super speed, while Weaken + Poison => Increase damage taken. It's just a ideia I had tho.
Good job!