Underfell Sans Fight is an undertale AU with bad monsters, in the pacifist route, you must spare monsters and make them good people, in the genocide route, you must KILL everyone.
In this fight, you are a genocider, you must kill.
My screen is like stuck in a small window. Your browser doesn't appear to support the HTML5 element. Controls: any to start the next message(once the last has ended) X to skip to the end of the.
Tips for fighting:
In phase 1, try your best not healing, try your best dodging the attacks.
Never let your guard down.
Keep fighting.
Don't use mercy, EVER, it won't work even in Sans's break, because nothing will happen, so it's a waste of god damn time.