Very Very cool.
Though i'd say the fact that you often lose your ghosts when failing meaning you have to grind dying repeatedly to get back to full force, makes this far more annoying than it should be.
that and having seemingly no control over the ghosts, losing a run you grinded for because the ghosts flew off screen and got shot is super disheartening.
i reckon a version of this where you could guide the spirits somewhat, and you didn't lose all your progression when you fail badly, could be an absolutely sick game.
i'm very impressed, even though i didn't manage to kill the ring firing monks a single time