Bad Time Simulator

Controls I checked

Give the game one click before anything else; until then it ignores your keys. The opening screen reads Select your bad time, with Normal, Practice, Endless, Single attack, and Custom attack. The cursor slides with Up and Down. Z picks a line, and Enter does the same.

Normal throws you straight into the fight after a short ready bubble. Practice keeps you going after a loss and flashes FAILURE at the top instead of ending the run. Endless keeps the patterns coming, Single attack lets you drill one, and Custom attack loads patterns people write themselves.

Inside the board, a red heart glides freely on all four arrows. When the heart turns blue, gravity takes over: it drops to the floor, and Up is your jump.

The build has its own touch controls. In an Android-emulated Chromium check on 22 October 2026, on-screen A/B buttons appeared and tapping A started the opening. We did not complete a touch-only battle or test physical phones; a keyboard remains the recommended setup for precise blue-soul jumps.

What you're up against

Sans is the last boss of Undertale's Genocide Route. He waits in the Last Corridor, skips judgment, and opens fire. Serious Mode is on, and unlike almost every other boss he goes first, so the opener lands before you touch the menu.

He calls that opener his strongest move, and it comes in three stages. A blue slam pins you to a bone floor. Your heart goes red again while a bone wall rolls across, leaving one thin slot to thread. Last come Gaster Blaster volleys, four of them: flanks, a corner cross, flanks once more, then two giant skulls whose beams fill almost the whole board.

Watch the purple KR next to your HP. KARMA keeps chipping away after a bone touches you, one point per frame, and every attack except his telekinesis applies it. Getting clipped twice in a row hurts far more than the hit itself.

Megalovania drives the whole battle. Toby Fox composed it, and it is the track tied to this fight.

Survival tips

• Be ready on frame one. The opening slam comes right after the ready bubble, with no warm-up turn.
• Get out of a pattern fast once you're hit. KR drains while you stay in contact, so leaving early saves more HP than tanking through.
• Blasters show their skull before the beam. Read where the mouth points, then step off that line before it fires.
• On blue turns, watch the lid as well as the floor. Long bones hang from the top, so an oversized jump can hurt as much as a late one.
• In the real game, healing is limited to the food you carry, and eating during KR wastes it. Let KR run out, then eat.
• Use Practice to learn the order. A death there just restarts the pattern, so you can drill the blaster rings without the walk back.

Hard mode and custom attacks

There is no separate hard mode on the menu. The hardest pick is Endless, which keeps the patterns coming until you drop. Some built-in attacks also have harder copies in jcw87's files, like sans_platforms4hard, sans_bonegap1fast, and sans_platformblasterfast.

Custom attack runs patterns people write themselves. jcw87 posted a custom attacks guide in the GitHub repo. Each attack is a CSV file: the first column is a delay in seconds, the second is the function name, and the rest are its arguments. The guide suggests writing it in a spreadsheet and saving as CSV. Every attack has to call EndAttack, or it never ends.

Two Sans games, two builds

They are two different fan games. Bad Time Simulator is jcw87's Construct 2 clone of the Genocide battle: KARMA, blue gravity, the blaster rings, and a menu for Normal, Practice, Endless, and single attacks. It runs at 640 by 480 and has no Sans dialogue.

Our Sans Fight Simulator is a separate Scratch project by S00TF00T, with corridor talk and its own orange, white, and purple soul challenges.

Deltarune Fight keeps its own copy of Bad Time Simulator .

Want the other Genocide boss? Try the Undyne the Undying fight simulator .