Monsterize {Napstablook x OC}

'Monsterize'
"To make something or another into a monster or the appearance of."

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Not every human despised the monsters, some truly loved them, and that has let to the creation of something that can save the monsters from the Underground.

What if this creation could make something like a humanlike soul for itself? It would be the last soul necessary to break the barrier.

But what if with the way it developed its human soul, may just be the way to alter it to a monster soul?
Intentionally or not with the help of a certain music-loving ghost.