About Bad Time Simulator
Bad Time Simulator is a free, browser-based fan game that recreates the battle atmosphere of the Sans encounter from Undertale (2015), the indie RPG created by Toby Fox. It runs entirely in your web browser with no installation required — just open the page, press a key, and the fight begins.
What Is This Game?
The Sans boss fight in Undertale is widely regarded as one of the most challenging and memorable moments in indie gaming history. Players dodge relentless bone attacks, navigate the Blue Soul gravity mechanic, and face screen-clearing Gaster Blasters — all set to the iconic Megalovania soundtrack.
This fan project captures the core of that experience in a self-contained browser game. It is built from scratch using only modern web technologies — no game engines, no external libraries, no audio files. Every visual effect and every musical note is generated procedurally in real time.
Technology Stack
Everything you see and hear is created on-the-fly using standard web APIs:
- HTML5 Canvas API — all game rendering (sprites, attacks, UI) at 500 × 500 native resolution, scaled responsively via CSS.
- Web Audio API — procedural sound effects (oscillators + white noise) and a real-time chiptune music sequencer that plays a Megalovania-inspired track without any audio files.
- Vanilla JavaScript (ES5 strict mode) — no frameworks, no dependencies. The entire game logic is contained in ~1,000 lines of hand-written JS.
- CSS3 — responsive layout, sticky navigation, backdrop-filter blur, CSS animations, and mobile-first breakpoints.
- Press Start 2P — the pixel-style font loaded from Google Fonts, giving the game its authentic retro aesthetic.
The music sequencer runs on a 16th-note grid at 120 BPM, scheduling oscillator nodes 150 ms ahead to prevent audio glitches — a technique known as the Web Audio clock pattern.
Key Features
- 6 distinct attack patterns that cycle and increase in speed
- Authentic Blue Soul gravity mode — bones only damage a moving soul
- Gaster Blaster charge → fire animation with Karmic Retribution (KR) damage
- Procedural chiptune Megalovania (square wave lead, triangle harmony, sawtooth bass, drum kit)
- 10 procedural SFX: typewriter ticks, hit noise, blaster charge, game over melody, and more
- Mobile-friendly with an auto-showing on-screen D-pad for touch devices
- Invincibility frames after a hit (soul blinks for 0.65 s)
- Fully accessible navigation and ARIA-labelled interactive elements
Fan Game Disclaimer
This project is an unofficial, non-commercial fan game. It is not affiliated with, endorsed by, or sponsored by Toby Fox, the Undertale franchise, or any associated publisher or rights holder. Undertale™ and all related characters, names, music, and concepts are the intellectual property of Toby Fox. No copyright infringement is intended. This game does not reproduce any original Undertale assets — all code, graphics, and audio are independently created.
Fan games are a beloved tradition in gaming culture. This project exists purely as a creative tribute to a game that has inspired millions of players worldwide. If you enjoy this fan experience, we strongly encourage you to play and support the official Undertale game by Toby Fox, available on Steam and other platforms.
Frequently Asked Questions
Is this game free?
Yes — completely free. No account, no in-app purchases, no ads. Open the page and play instantly in any modern browser.
Does it work on mobile?
Yes. The game detects touch devices automatically and displays a virtual D-pad and action buttons. It is tested on iOS Safari and Android Chrome.
Can I share or embed this game?
You are welcome to share the link. If you wish to embed or redistribute the source code, please note the fan-game disclaimer above and ensure proper attribution.
Will new features be added?
This is an ongoing fan project. Potential future additions include a high-score leaderboard, additional attack phases, difficulty settings, and accessibility options. No timeline is confirmed.
How is this different from other Bad Time Simulator versions?
This version is built entirely from scratch with no copied code or assets. It features procedurally generated audio (no MP3 files), a fully responsive layout, and modern accessibility practices — distinguishing it from older Flash-era fan games.