Do you wanna have a bad time? This is the famous Undertale Sans boss fight, rebuilt as a free browser game. Dodge bone walls and Gaster Blasters, watch for the blue attacks you must stand still through, survive the KR poison, and land your hits during Sans’ turn — all set to MEGALOVANIA. No download, no install, just click and fight.
This is a 1:1 recreation of the hardest fight in Undertale. You control the red soul inside the box while Sans throws attack after attack at you. Unlike every other Undertale fight, Sans has no mercy button that works — your only way out is to survive his turn order and attack when the menu appears.
Sans makes a brief cameo in DELTARUNE Chapter 1, but his legendary boss fight belongs to Undertale. Bad Time Simulator is a faithful fan-made recreation by Jcw87, hosted on this page for Toby Fox fans who want the crossover challenge. It reproduces the full genocide-route encounter: the intro line, the bone slams, the Gaster Blaster barrages, and the final attack where Sans throws you against the walls.
Yes. Bad Time Simulator includes touch controls, so the on-screen movement pad and action buttons appear on phones and tablets.
Keyboard is the intended control scheme — arrows or WASD to move and Z/Enter to confirm. The page also passes gamepad input through when your browser supports it.
The game starts with the sound on and MEGALOVANIA playing from its first action. If your browser blocks autoplay audio, click once inside the game to enable sound.
No — this is an unofficial fan recreation. Undertale was created by Toby Fox, and Sans belongs to the Undertale series. The original fan project is Bad Time Simulator by Jcw87.
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The Sans fight — now playable
Dodge bone walls and Gaster Blasters, survive the KR poison, and land your hits to MEGALOVANIA. Free in your browser, no download.
FIGHT SANS