* you're gonna have a bad time.
Fan-Made · Not affiliated with Toby Fox or Undertale™
Bad Time Simulator is a free fan-made browser game inspired by the legendary Sans boss fight from Undertale (created by Toby Fox). No download, no sign-up — just open the page and play directly in your browser on desktop or mobile.
Experience the Sans boss fight from Undertale in your browser. Dodge bones, avoid Gaster Blasters, and survive Blue Soul mode as attacks get faster each phase. This fan game captures the challenge and style of the original encounter — play anytime, no install needed.
Use WASD or arrow keys to move your soul; Z or Enter to confirm. Six attack patterns include bone rain, horizontal sweeps, Gaster Blaster beams, bone walls, and the gravity-based Blue Soul section. Each phase speeds up — see how long you can last. Full controls and tips are in the How to Play guide.
Yes. Bad Time Simulator is completely free. No download, no sign-up, no account, and no in-app purchases. Open the page in your browser and play the Undertale Sans boss fight fan game instantly.
Use WASD or arrow keys to move your soul during attacks. Press Z or Enter to confirm (dialogue, menu, FIGHT). Press X or Escape to cancel. On mobile, use the on-screen D-pad and Z/X buttons. Press M to mute music.
Yes. Bad Time Simulator is mobile-friendly. On touch devices, an on-screen D-pad and action buttons (Z, X) appear automatically. The game runs in the browser on phones and tablets with no app install required.
Bad Time Simulator features six attack types: Bone Rain (falling bones), Bone Sweep (horizontal sweeps), Gaster Blasters (laser beams), Bone Walls (gaps to dodge through), Blue Soul mode (gravity — stand still on blue bones), and Diagonal bone attacks. Phases get faster as you progress.
No. Bad Time Simulator is an unofficial fan-made game. It is not affiliated with, endorsed by, or sponsored by Toby Fox or the official Undertale game. Undertale™ and all related characters are the property of Toby Fox. This is a tribute fan project only.
In Blue Soul mode, gravity pulls your soul down. Move left and right with the arrow keys or D-pad. Blue bones only damage you when you are moving — stand completely still as blue bones pass through to avoid damage. Jump with Up when you need to reach a safe spot.
Disclaimer: This is an unofficial fan game created for educational and entertainment purposes. Undertale™ and all related characters are the property of Toby Fox. This project is not affiliated with, endorsed by, or sponsored by Toby Fox or any official Undertale entity. No copyright infringement is intended.