Bad Time Simulator: The Original Sans Battle by Jcw87
Play the original Construct 2 Sans fight simulation. Choose between Normal mode, Practice trainer, Endless survival, or practice any of the 23 attacks individually with full sound and physics.
How to Master Bad Time Simulator in 3 Steps
Select Your Mode
Pick Normal for the authentic story battle, Practice for infinite HP training, or Single Attack to drill specific difficult moves.
Master the Red & Blue Soul
Red Soul moves freely in all directions. Blue Soul obeys heavy gravity, requiring precise jump heights over bone gaps and onto moving platforms.
Never Choose SPARE
When Sans offers mercy at the mid-fight break, selecting SPARE leads to an instant, unavoidable game over. Choose ATTACK or ITEM instead.
The Complete Guide to the Sans Genocide Boss Fight
Originally created with Construct 2 by developer Jcw87, Bad Time Simulator is universally celebrated as the most faithful and precise web adaptation of Undertale's ultimate boss encounter.
The 5 Game Modes Explained
- Normal: The complete 2-phase battle exactly as it appears in Undertale, including the dialogue sequences, the fake sparing mercy trap, and the legendary final attack.
- Practice: Grants unlimited health, allowing players to practice timing and evasion patterns without ever seeing the Game Over screen.
- Endless: An infinite endurance mode that continuously throws randomized bone columns and Gaster Blasters at increasing speeds.
- Single Attack: An indispensable training tool that lets you choose any of Sans's 23 individual attack waves to master on demand.
- Custom Attack: Load custom community-made attack CSV files to design and play your own bullet-hell patterns.
Understanding Karma (KR) and Zero Invincibility Frames
Every other boss in Undertale gives you temporary invincibility after taking damage. Sans breaks this rule: he attacks at 30 to 60 hits per second, draining your health constantly while inflicting Karma (KR) poison. Survival depends strictly on flawless movement and minimizing every frame of contact with hazards.
Sans Attack Patterns & Survival Matrix
Breakdown of key attack phases and optimal dodging strategies in Bad Time Simulator:
| Attack Name | Soul Color | Hazard Type | Difficulty | Recommended Evasion Strategy |
|---|---|---|---|---|
| The Opening Slam | Blue Soul | Gravity slam + Blaster cross | Extreme (9/10) | Hold UP key prior to match start; weave left/right through the rising bones. |
| Blue Bones | Red Soul | Alternating white & blue bones | Moderate (6/10) | Hop over white bones, then release all movement keys to let blue bones pass through. |
| Platform Bone Tunnel | Blue Soul | Moving platforms over bone bed | Hard (7.5/10) | Perform short controlled hops between platforms; avoid jumping into ceiling bones. |
| Gaster Blaster Wheel | Red Soul | Rotating circular laser beam | Brutal (8.5/10) | Circle continuously along the outer boundary wall in a smooth clockwise loop. |
| The Special Final Attack | Blue & Red | Wall slams, bone tunnel, mega blasters | Legendary (10/10) | Counter gravity slams in opposite direction; sprint continuously in the final circle. |
Frequently Asked Questions
Yes. This page runs the official, original game engine developed by Jcw87, complete with the opening menu (Normal, Practice, Endless, Single attack, Custom attack) and authentic audio.
Click inside the game screen or press the 🎯 Focus Game button in the toolbar above. This locks your keyboard input directly into the game canvas so your browser will not scroll.
Click the ⛶ Fullscreen button located right above the game screen, or press F4 on your keyboard while the game is focused.