I didn't write this but I have been given permission to post this all credit goes to Valentinesdaygreen and a link below to the original story origin http://valentinesdaygreen.deviantart.com/

The reader is a wizard, beings with the shape of humans but the magic of monsters. Wizards were forced into the war between humans and monsters by the humans. There, she meets the monster general, Grillby. Cover photo belongs to: http://ask-grillby.tumblr.com

You were working with Alphys in the lab in Undertale when chaos strikes! In a freak accident, concentrated determination is mixed with an unnamed concoction and blow you through a dimensional rift. When you reawake, you find yourself in what seems to be the beginning of Undertale once again. Upset but not overly surprised, you make your way back to Alphys's lab... Only to find her lab assistant is no longer you! Working with Alphys now is a tall, punkish skeleton with two cracks in his skull and a snarky attitude. As they help you find your way home, will you find more than that? *I DO NOT OWN UNDERTALE OR GASTERTALE!!! I WISH I DID BUT I DO NOT! THIS IS JUST A FANFICTION!!*