This page may be considered as a spoiler for the game, which sucks since the game hasn't even come out yet. You may follow the warning like a good user...unless you wanna have a bad time....
You've been warned!
Underswap is an alternate universe of Undertale created by Popcorn Pr1nce. It revolves around switching the personalities of roles of different characters. While not every character has been swapped, most characters do swap with another (except Jerry, who stays the same). Some people believe Underswap to be made by Team Switched but it wasn't, instead it was inspired by Popcornpr1nce.