Bad Time Simulator

Bad Time Simulator is a browser remake of the Sans boss fight from Undertale's Genocide route. There is no exploring, no levelling, and no choice to make: the game drops you straight into the last corridor with one heart, 92 HP, and a skeleton who has already decided you are not leaving.

Everything that made the original fight famous is here — the flickering eye, the bad puns, the escalating bullet patterns, and a theme that starts as a joke and ends as a countdown. The build is a Construct 2 export, so it loads in seconds and plays entirely with the keyboard.

Who Sans is in Undertale

Sans is the short skeleton in the blue hoodie who greets you at the beginning of Undertale with bad jokes and a hot dog stand. He is lazy, friendly, and apparently harmless, which is exactly why the fight works: the game spends hours teaching you that he will not lift a finger, then puts him in your way as the final boss.

In that fight he never attacks with a weapon. He dodges, he remembers how many times you have died, and he uses bones, gravity, and Gaster Blasters instead of a knife. Bad Time Simulator takes that single encounter and turns it into a standalone game, so you can practise the patterns without replaying an entire route to reach them.

Soul modes and how Sans attacks

Your soul is the small heart inside the box. Sans changes the rules of how that heart moves, and the fight is built on switching between those rules quickly.

The red soul

This is the default mode. The heart floats freely in eight directions, has no gravity, and moves exactly as fast as you push it. It is the most comfortable mode and also the most exposed: nothing protects you, so a single bone or beam that connects takes HP away.

The blue soul

Here gravity turns on. The heart falls to the floor of the box and you jump instead of floating, and holding a direction pulls you down faster than tapping it. Blue attacks also stop hurting you as long as you keep the heart still, which is the opposite of the instinct the rest of the fight trains.

The attacks you will see most

• Gaster Blasters: floating skulls charge for a moment and then fire a straight beam. The beam does not track, so the safe move is a short step off the line rather than a sprint across the box.
• Bone walls: vertical and horizontal bones slide across the box or stab into it. Long walls usually come with a gap; look for it before you start moving.
• Gravity slams: the box drags the soul toward one wall while projectiles arrive from the other side, forcing you to move against the pull instead of with it.

How to fight Sans in Bad Time Simulator

Dodging is most of the game. Sans attacks in a fixed order, so the fight is closer to learning a song than to fighting an enemy: the first time a pattern appears you lose HP, the third time you recognise the opening, and by the fifth you are already moving before the bones do. Do not try to win on reflexes alone — the patterns are faster than reaction time by design.

Keep the heart alive

The bar under the box is your HP, and the purple KARMA bar next to it is damage that is still being applied. Standing still in a beam poisons you twice: once when it hits and again every frame afterwards. If the KARMA bar is filling, break line of sight first and heal second.

Use the four buttons

• FIGHT: your only way to damage Sans, and it only works while he is asleep. A missed swing costs nothing except the turn, so take the shot as soon as he dozes off.
• ACT: mostly flavour here, but Check tells you what a pattern is doing when a new one catches you off guard.
• ITEM: the healing items you start with are limited. Use one when KARMA is high, not when HP is merely low, or you will burn them all in the first half.
• MERCY: sparing does nothing. This is not a fight you can talk your way out of.

Modes in Bad Time Simulator

The main menu is not a formality — the modes change how long a session lasts, and they are worth choosing deliberately.

• Normal: the full fight in order, both phases, no shortcuts.
• Practice: the same patterns with more room to breathe, which is where most players learn the second phase.
• Endless: a survival loop that keeps the attacks coming until the heart breaks, good for measuring whether you are actually improving.
• Single Attack: pick one pattern out of the 24 and repeat it until it stops being scary.
• Custom Attack: the slot exists for player-made patterns, though it is empty in most builds.

The 24 attacks

The fight is built from 24 attack scripts, split into two halves: 13 in the first phase and 11 in the second. The second half is not simply faster — it mixes modes, so a blue-soul jump section can turn into a gravity slam without a pause in between. If you are stuck, Single Attack mode plus the attack name in the corner of the box is the fastest way to isolate the one pattern that keeps killing you.

Frequently asked questions

Who made Bad Time Simulator?

The fight is a fan project by the developer jcw87, built as a Construct 2 remake of the Sans encounter from Undertale, which was created by Toby Fox. The original browser version, sometimes credited to pokemaster2005, has been circulating since the late 2010s. This page hosts its own copy of the build so the game keeps working even if the original host goes down.

How many attacks does Sans have?

Twenty-four, divided into 13 in the first phase and 11 in the second. They include bone walls, bone slams, Gaster Blaster volleys, platform sections, and the final pattern that ends the fight.

Do I need to have played Undertale first?

No. The game explains nothing, but it also spoils nothing beyond the fight itself. The only thing you need to know is that the heart is you, and blue bones only hurt if you move.

Can I play it on a phone?

The build includes on-screen directional and action buttons, so it runs on mobile browsers, though the second phase is genuinely hard without a keyboard. Arrow keys or WASD move, Z or Enter confirms, X cancels and attacks.

What happens when you beat Sans?

He dies, the room goes quiet, and the fight ends — there is no reward screen and no epilogue. Beating him is the whole point, and the only thing left to do afterwards is pick a harder mode and start again. If you run out of HP, the heart shatters and you restart from the beginning of the selected mode.

If you want more keyboard-heavy action in the same spirit, browse the rest of the action games on cool games spot — everything there runs in the browser with no install.