Hello~ Can you please help me? I'm kinda lost

Just remembered my very favorite au of all time. Decided to make all the main characters form there. I'm still opened for requests. Would be nice actually.

P.S. no windings this time, because I make it as a person, not as a Gaster.

Story:

It's quite simple. You replace a first monster that Frisk encountered. Be scary, be nice, be whatever.

Warning: all characters exceeded age of 18 years.