About Bad Time Simulator
Bad Time Simulator is an independent browser gaming website dedicated to Undertale, Deltarune, and fan-made boss battles. Whether you want to challenge Sans again, discover an unusual Alternate Universe (AU), or try a community-created fight, our goal is to make these experiences easier to find, play, and understand.
Who We Are
Bad Time Simulator began with a simple idea: players shouldn't have to search through scattered project pages just to find a particular boss fight. Many Undertale and Deltarune fan games are distributed across different websites, engines, and community platforms. Some are easy to launch, while others require additional steps or are difficult to find.
We bring together a growing collection of browser-playable games and organize them in one place. This is an independently maintained fan-game website, not an official Undertale or Deltarune product.
What You'll Find
Our game library focuses on recognizable battles, creative fan interpretations, and challenging encounters inspired by the Undertale and Deltarune communities.
- Undertale Boss Battles: Encounters inspired by characters such as Sans, Flowey, Asgore, and other familiar faces.
- Deltarune Battles: Fan-made and recreated encounters featuring characters, battle systems, and mechanics associated with Deltarune.
- Undertale AU Games: Alternate Universe interpretations, including unusual versions of familiar characters and multi-phase boss fights.
- Sans Battles: A collection of Sans-related simulators featuring different attack patterns, difficulty levels, and fan-created variations.
You can start with our Bad Time Simulator homepage or explore the full collection through All Games.
How We Organize Games
Finding the right game is not always as simple as searching for a character's name. Several fan projects may feature the same boss but offer very different gameplay. One version might focus on a single battle, while another includes additional phases, modified attacks, or a completely different combat system.
We organize games by series, characters, and related categories to make browsing easier. Individual game pages may include controls, gameplay explanations, available modes, and practical tips. When relevant information is available, we also try to distinguish between similarly named projects and different versions of a battle.
Playing Games in Your Browser
Many games in our collection can be launched directly from their individual pages without installing a separate application. Depending on the project, a game may run through a browser-based engine, a web-compatible build, or an embedded game player.
Compatibility varies between projects. Some games work well with keyboard controls on desktop computers, while others also support mobile devices. Loading times and available controls may differ depending on the original game's engine and design. Check each game's instructions for the most relevant information.
Fan Projects and Original Creators
Undertale and Deltarune have inspired a remarkable community of developers, artists, musicians, and game designers. The variety of fan-made battles is a major reason this collection exists.
We do not claim ownership of third-party games, characters, artwork, music, or other materials. These remain the work or property of their respective creators and rights holders. Bad Time Simulator is not affiliated with or endorsed by Toby Fox or the official creators and publishers of Undertale and Deltarune.
If you are a creator and believe a game has been incorrectly attributed, or if you have concerns about how your work appears on this website, please contact us.
Help Us Improve the Collection
We want the site to remain useful for players looking for particular battles, versions, or gameplay experiences. Reports about broken games, incorrect descriptions, missing credits, and confusing controls help us identify what needs attention.
Found an issue or have a game suggestion? Visit our Contact Us page to get in touch.