The role of Sans is filled by his brother Papyrus, a laid-back but talented skeleton who first meets Chara upon their entry into Starlight Isles, supervising Sans's antics throughout the region.

He's the star of Ruined Home, adored by the many monsters who dwell within.

The role of Napstablook is filled by Mettacrit, a ghost who blocks Chara's way in Ruined Home and acts as the third miniboss of the game.

A vindictive monster who lashes out against everything around them.

The role of the Tutorial Dummy is filled by the Mad Dummy, a ghost who lives inside a training dummy and acts as the unwilling tutorial enemy for Chara in the fangame.

The role of Toriel is filled by Asgore, a goat monster who acts as the caretaker of Ruined Home, saving Chara near the start of the game from Temmie's attack.

The role of Flowey is filled by Temmie, a seemingly-ditzy dog/cat monster who attacks Chara when they first meet in the Underground.

The role of Frisk is filled by Chara, a human child and the main protagonist who falls into the Underground after climbing Mt.

Asgore's home in Ruined Home contains a garden as well as a waterwheel that powers his house.

Minor details were added to the game based on unused concepts, designs, artwork, sprites, and music by Toby Fox.

New Home is replaced with The City of New.

Hotland (Summer) is replaced with Boreal Bluffs (Winter).

Waterfall (Spring) is replaced with Crystal Springs (Autumn).

Snowdin (Winter) is replaced with Starlight Isles (Summer).

The Ruins (Autumn) is replaced with Ruined Home (Spring).

The seasonal representation of different locations in Undertale have been changed.

The fangame itself was created with by the developers with an original experience from the source Undertale game in mind, as well as out of a dissatisfaction for the personality-swapping of characters in the popular interpretation of Underswap. Team Switched's Underswap is an alternate interpretation of the popular AU which preserves the original personalities of the swapped characters and expands on their roles to a great extent.

Underswap flowey