Undertale: Underfell for Windows

Quick overview

Undertale: Underfell is a fan-made, character-focused RPG set in an alternate version of Undertale where the inhabitants are hostile rather than harmless. It uses retro-style visuals and requires tactical thinking during encounters. The experience is single-player and tailored mainly to people familiar with Undertale, although its straightforward mechanics and strategic combat can appeal to new players as well.

Origins and official status

Underfell began as a visual concept depicting a darker, “edgier” alternate universe of Undertale and was later expanded into a playable fan project by The THI Team (THI Games). It is an unofficial, non-commercial tribute to the original title—created outside of the original developer’s official releases.

Purchasing and demo options

There is a limited demo and a more complete release. To access the entire game you will need to obtain the full version; the demo gives only a brief taste of the content and mechanics.

How to install and launch

• Download the Windows executable and run it on a Windows 10 PC.
• The game launches immediately after you run the file; it does not automatically create a desktop shortcut.
• On startup the game displays a spoiler warning for Undertale and recommends playing or watching Undertale first so new players can better appreciate the altered world.

The setting and main plot points

Long ago, humans and monsters fought a catastrophic war. Humans ultimately sealed the monsters beneath the surface with magic. In this AU you play as Frisk, a child who falls into the caverns beneath Mount Ebott. The initial goal is to navigate the underground and find a way out, with Flowey acting as an early guide. Many familiar faces return but with twisted personalities: for example, Fell Sans is an antagonistic figure, while Papyrus takes on a far more domineering role than in the original game.

Gameplay basics and controls

• Movement: arrow keys
• Interact: Z
• Cancel: X
• Menu: C

Combat is more aggressive than in Undertale; monsters are often hostile, and encounters can be tougher. HP is a finite resource—if it hits zero, the run ends. Dialogue and important information are displayed on-screen in clear text, and chiptune-style music supports the retro atmosphere. Player choices influence relationships and story branches, leading to different outcomes on repeated playthroughs.

Community spin-offs and related fan projects

• Trainertale — a crossover AU blending elements of Pokémon with Undertale.
• Underfell: Revolution — a fan project that unfolds across two distinct locations.
• Sans Simulator — a free fan-made battle game focused on Sans-style combat.
• Unitale — a toolkit and AU that allows custom encounters and mods.
• Deltarune — a related title from the original creator that explores a different narrative.
• Underswap — an AU that swaps character roles and personalities.
• Undertale: The Second Chance — another fan-created alternate storyline.

These and other fan works demonstrate how the community expands and reinterprets the Undertale universe in many directions.

Fan culture and theories

Because Underfell originated largely from aesthetic concepts rather than detailed canonical backstories, fans have filled in gaps with their own explanations and headcanons. The stripped-down lore invites speculation about character motivations and the reasons for their darker traits, which helps keep the community engaged.

Who will enjoy this AU

Longtime Undertale fans are most likely to get the most out of Underfell, enjoying comparisons between the original characters and their corrupted counterparts. Newcomers might find the dated graphics less appealing, but the tactical combat and straightforward systems can still provide an entertaining experience.