HOT Bad Time Simulator (v1.0.8 WebGL) is live! Fully compatible with School Chromebooks, 60 FPS Desktops & Mobile Touchscreens.
GENOCIDE ROUTE CLIMAX SIMULATION

Bad Time Simulator: Sans Fight Online

Do you wanna have a bad time? Step into the Judgment Hall and face off against Sans in the ultimate high-precision HTML5 web simulator. Recreated with authentic 60 FPS physics, Karmic Retribution (KR), customizable attack drills, and unblocked browser gameplay.

ENGINE: CONSTRUCT 2 / WEBGL (60 FPS)

Touch buttons emit native keyboard events directly to the battle box.

Movement: ▲▼◀▶ or WASD Select / Attack: Z or Enter Cancel / Slow: X or Shift
● Click inside the game box if controls are not responding!
Boss Opponent
Sans the Skeleton
Combat Difficulty
10 / 10 (Insane)
Total Gauntlet Turns
23 Intense Turns
Damage System
Karmic Retribution (KR)

#01 What is Bad Time Simulator? History & Legacy

Bad Time Simulator is the world’s most celebrated fan-made web browser recreation of the climactic Sans boss battle from Toby Fox’s groundbreaking 2015 indie RPG, Undertale. Originally crafted by visionary developer Jcw87 using the Construct 2 HTML5 game engine, this project solved a massive problem for the worldwide gaming community: allowing players to master gaming’s most demanding bullet-hell showdown without needing to replay hours of the harrowing Genocide Route just to reach the final corridor.

In the narrative lore of Undertale, reaching Sans requires systematically clearing every monster across the Ruins, Snowdin, Waterfall, and Hotland until "nobody came." Upon entering the majestic Last Corridor (the Judgment Hall), the cheerful, ketchup-loving skeleton turns into an insurmountable wall of retribution. Armed with gravity-manipulating psychokinesis, devastating Gaster Blasters, and an unforgiving rule-breaking combat interface, Sans became an overnight gaming icon and a viral streaming sensation.

Hosted on GitHub Pages at bad-time-simulator.github.io, this simulator delivers an authentic 1-to-1 conversion of Sans’ complex attack animations, sound effects, soul physics, and frame-perfect collision detection. Whether you are an aspiring speedrunner drilling the final attack, a casual fan wanting to experience the iconic "Megalovania" battle firsthand, or a student seeking unblocked gameplay on a Chromebook, this web portal serves as your definitive training ground.

💡 Why Did Bad Time Simulator Become an Internet Phenomenon?

Unlike the base game, where a single defeat requires restarting dialogue sequences and sitting through slow menus, Bad Time Simulator lets you instantaneously restart, loop individual attacks infinitely, and toggle practice options. Over 25 million players across YouTube, Twitch, and Reddit have utilized this web port to test their limits.

#02 Keyboard, Gamepad & Mobile Controls Reference

Winning against Sans demands millisecond precision. Bad Time Simulator supports multiple input methods, designed with zero input buffering to guarantee immediate twitch response. Review the primary key bindings below:

Arrow Keys / WASD NAVIGATION

Controls your Soul inside the bullet board. When in Red Soul mode, moves freely in all directions. When in Blue Soul mode, controls jumping against gravity.

Z / Enter / Space CONFIRM

Confirms battle selections (FIGHT, ACT, ITEM, MERCY), attacks during your turn, and skips through Sans’ dialogue boxes without wasting precious reaction time.

X / Left Shift CANCEL / PRECISION

Cancels out of sub-menus. In practice modes and modified builds, holding Shift can also trigger focus mode to slow soul movement for ultra-tight gaps.

F Key (Fullscreen) VIEWPORT

Toggles full-screen display mode. Highly recommended for maximum peripheral vision when dodging rotating Gaster Blaster lasers and jumping bone hurdles.

⚠️ Keyboard Ghosting Alert

Cheaper non-mechanical keyboards frequently suffer from "key ghosting" (failing to register 3 simultaneous arrow presses, e.g., UP + RIGHT while holding Z). If your soul feels sluggish during diagonal jumps, consider using an anti-ghosting mechanical keyboard or binding controls to WASD.

#03 Core Combat Mechanics: The Mathematics of KR

To understand why Sans is feared across gaming history, you must understand how he deliberately shatters every established combat rule in Undertale:

1. Karmic Retribution (KR) & Removal of Invincibility Frames

In standard Undertale boss fights, taking damage awards you roughly 0.5 to 1.0 second of invulnerability frames (i-frames), during which your heart flashes and cannot be harmed. Sans completely eliminates i-frames.

His attacks only deal 1 point of direct damage, but because the browser runs at 60 FPS, coming into contact with a bone or laser deals 1 HP of damage every single frame. Just half a second of collision strips away 30 HP! Furthermore, KR converts lost health into a purple toxic gauge. While the purple gauge does not instantly kill you, it decays downward at a steady rate of 1 HP every few ticks until your remaining health reaches 1 HP. If you are clipped by even a single rogue projectile while suffering maximum KR poison, you immediately perish.

2. Red Soul (Free Flight) vs. Blue Soul (Gravitational Physics)

Throughout the 23-turn trial, Sans repeatedly flashes his glowing cyan/yellow left eye and flicks his hand, instantaneously altering your Soul’s physics:

  • Red Soul: Omnidirectional free-floating movement at a constant velocity. Essential for threading through spiraling Gaster Blasters and dodging bone skewers.
  • Blue Soul (Gravity Mode): Subject to artificial gravitational pull. The direction of gravity can suddenly flip to the floor, ceiling, left wall, or right wall. Jumping height is variable: tapping the jump key creates a micro-hop, while holding it down produces a high leap.

3. The Three Bone Color Rules

  • White Bones: Standard physical hazards. Any physical contact rapidly drains your HP and inflicts KR poison.
  • Blue Bones: Cyan-colored bones that pass harmlessly through your soul only if you are completely stationary. If you press any movement key while touching a blue bone, you will suffer catastrophic damage.
  • Orange Bones: Must maintain continuous movement to avoid receiving damage.

#04 Interactive KR Damage & Survival Calculator

Curious how long your 92 HP would last inside Sans' bone cage? Use our interactive simulation below to observe how frame collisions translate into lethal Karmic Retribution damage:

⚡ SANS DAMAGE ENGINE (60 TICKS / SEC) Base HP: 92 (LV 19 Frisk)
Direct HP Remaining: 67 / 92 KR Poison Stored: 25 HP Outcome: SURVIVED

#05 Sans Attack Roster Breakdown

Sans utilizes four distinctive weapon archetypes to overwhelm your senses. Recognizing the startup frames of each attack allows you to position your soul preemptively:

Gaster Blasters DESTRUCTIVE

Floating draconic skull apparitions that materialize in empty space, target your coordinates, open their jaws, and emit a colossal column of energy. Listen for the iconic charging chirp!

Bone Waves & Stems RHYTHM

Rhythmic columns of white bones scrolling across the top and bottom of the board. Requires precise horizontal jumping between platforms while timing short and long hops.

Gravity Wall Slams REFLEX

Sans violently flings your soul against the arena walls. As soon as your heart contacts the boundary, razor-sharp bones shoot upward from that exact surface. You must immediately press the opposing jump key.

Menu UI Infiltration META-ATTACK

Breaking the 4th wall entirely, Sans summons bones that actively patrol through the FIGHT, ACT, ITEM, and MERCY buttons during your decision turn. Failing to dodge while choosing an item deals heavy KR!

#06 Complete 23-Turn Step-by-Step Survival Walkthrough

The battle against Sans is divided into two distinct phases separated by an infamous psychological trap. Here is the definitive roadmap to conquering every single turn:

PHASE 1: THE OPENING TRIAL (TURNS 1 – 12)

TURN 01: THE STRONGEST ATTACK
The Notorious Opening Gauntlet

Sans opens the battle immediately without waiting for your turn. He slams your soul downwards, summons a floor of bones, launches a wave of blue/white obstacles, and surrounds you with a ring of 6 Gaster Blasters.

Survival Tactic: Pre-hold UP on your keyboard during the black screen before the fight loads! The instant you jump over the rising floor bones, steer through the gap in the scrolling bone wave, then drift calmly toward the center to avoid the crossfire of the outer Blasters.
TURNS 02 – 06: PLATFORMS & SHORT HOPS
Low-Bone Hurdles & Moving Platforms

A sequence of horizontal scrolling platforms with alternating high and low bone ceilings. Hitting the ceiling or dropping into the pit is fatal.

Survival Tactic: Practice "micro-tapping" the UP arrow. Never execute a full-height jump when low bones are passing overhead. Let moving platforms carry your soul rather than frantically moving against the conveyor direction.
TURNS 07 – 11: LASER TUNNELS & BLUE COMBOS
Stationary Blue Bones & Rapid Blaster Sweeps

Sans mixes giant vertical cyan bones with rapid-firing diagonal Gaster Blasters.

Survival Tactic: Whenever a blue bone cuts across your screen, completely remove your fingers from all directional arrows. Remember: movement equals death. Tap arrows only when realigning between laser beams.
TURN 12: THE INTERMISSION (DEATH TRAP!)
Sans' Mercy Offer: "Geeettttttt Dunked On!!!"

Sans stops attacking, lowers his arms, wipes sweat from his brow, and offers you mercy: "if we're really friends... you won't come back." The game presents you with the option to SPARE him.

CRITICAL WARNING: DO NOT PRESS SPARE! If you choose MERCY -> SPARE, Sans immediately locks your soul in an unavoidable bone cage, plays cheerful music, and wipes out all 92 HP with the game over screen reading "geeettttttt dunked on!!!" You MUST choose ATTACK or heal with an ITEM to trigger Phase 2.

PHASE 2: THE UNLEASHED GAUNTLET (TURNS 13 – 22)

TURNS 13 – 17: SCREEN BLACKOUTS & MENU BONES
Randomized Teleportation & UI Bone Traps

The screen flickers black with ominous static sounds. Attacks are randomized in order and duration. Furthermore, white bones now crawl along your bottom menu buttons.

Survival Tactic: When selecting your turn, watch the bottom menu carefully! Hop your soul over the bones traversing FIGHT and ACT before pressing Z. During battle box flickers, immediately react to the audio cue of the upcoming attack rather than relying on visual warning lines.
TURNS 18 – 22: RAPID GRAVITY SLAMMING
Four-Way Psychokinetic Slamming

Sans rapidly jerks his hand Up, Down, Left, and Right. Your soul is thrown against the boundaries at supersonic speeds with spikes triggering on impact.

Survival Tactic: Hold down the arrow key opposite to the wall you are flying toward before you make contact. Buffer the jump input so that your soul rebounds off the wall the exact millisecond it touches.

TURN 23: SANS' "SPECIAL ATTACK" (THE FINALE)

TURN 23: SANS' SPECIAL ATTACK
The Infinite Gauntlet & The Laser Wheel

Sans unleashes his ultimate marathon offensive lasting over 45 uninterrupted seconds:

  1. Continuous gravity flips across horizontal bone corridors.
  2. A frantic sprint through a narrow bone-lined tunnel with razor-thin jump thresholds.
  3. The Laser Wheel: A giant ring of rotating Gaster Blasters circling around you while firing continuous beams.
  4. Violent multi-directional boundary slams that batter the battle box against the edges of your screen.
Final Survival Strategy: On the Laser Wheel, trace smooth, tight counter-clockwise circles directly around the center pivot. Do not hug the outer walls or you will clip into the laser origin point. After the slamming sequence ends, Sans will declare his special attack: literally doing nothing so your turn never begins!
🏆 How to Deliver the Final Finishing Strike

When Sans stops his turn, he attempts to trap you in an eternal stalemate. Remain calm and wait approximately 2 to 3 minutes as his dialogue slows down. Eventually, "Zzz" bubbles appear as Sans falls asleep. Push your Red Soul against the left wall of the battle box to physically push the entire UI frame down into the FIGHT button, then confirm your final attack!

#07 Bad Time Simulator Game Modes Explained

One of the primary reasons bad-time-simulator.github.io outclasses the original game for training is its extensive suite of built-in practice modes:

Normal Mode AUTHENTIC

The pure, unadulterated 23-turn Undertale experience. Standard HP, authentic dialogue triggers, and complete game-over states upon reaching zero HP.

Practice Mode TRAINING

Grants infinite or highly reinforced health pools with reduced KR poison rates. Perfect for newcomers learning the rhythm of complex platform jumps without constant game overs.

Single Attack Mode DRILL MODE

Allows you to select any of Sans’ 23 unique attack variants and loop it indefinitely. Master the Opening Slam, Menu Bones, or the Spinning Blasters until you can clear them blindfolded.

Endless Sans Mode SURVIVAL

A relentless procedural survival test where Sans generates endless waves of randomized attacks with increasing velocity. See how many seconds or turns you can survive!

#08 Comparison: Bad Time Simulator vs. Original Undertale

Feature / Metric Bad Time Simulator (Web) Undertale (Original Game) Fan AU Mods (Horrortale, etc.)
Frame Rate 60 FPS (Ultra-smooth WebGL) 30 FPS (Locked GameMaker Engine) Varies (30 – 60 FPS)
Attack Practice Selector ✔ Yes (Single Attack Loop) ✖ No (Full Fight Restart Only) Partial
Installation Required ✔ None (Instant Browser Play) ✖ Yes ($9.99 on Steam/Console) Requires Download
Chromebook & Mobile Support ✔ Yes (HTML5 + Virtual D-Pad) ✖ No (Windows/Mac/Console Only) Limited
Hitbox & Physics Accuracy 98.5% Authentic Match 100% Native Standard Heavily Modified / Unbalanced
Cost & Licensing 100% Free Fan Tribute Commercial Paid Video Game Free Fan Projects

#09 Pro Strategies for Achieving a "No-Hit" Clear

  • Fixate on Your Heart Hitbox, Not the Bones: Your soul’s collision hitbox is a tiny 4x4 pixel bounding box directly in the center of the heart sprite. As long as the center does not intersect a projectile, the edges of your heart can graze bones safely.
  • Buffer Wall Slams Early: When Sans flings his hand, you have roughly 150 milliseconds of travel time before collision. Hold down the rebound jump key before your heart touches the wall to launch away on frame 1.
  • Rely on Audio Beats: Toby Fox composed Megalovania with rhythmic cadence. Many of Sans’ Gaster Blasters and bone hops sync cleanly with the percussion of the soundtrack.
  • Utilize the Center Pivot on Spinning Blasters: On Turn 23's spinning laser wheel, do not try to outrun the lasers along the perimeter. Stay close to the center and rotate in tight circles to minimize total distance traveled.

#10 Unblocked Access & 60 FPS Browser Optimization

Because bad-time-simulator.github.io is hosted on GitHub's secure global CDN with clean SSL encryption, it naturally bypasses most educational and institutional network filters that block standard Flash and gaming portals.

🚀 How to Guarantee Stutter-Free 60 FPS on Low-Spec Chromebooks
  1. Enable Hardware Acceleration: In Google Chrome, go to chrome://settings/system and toggle "Use graphics acceleration when available" to ON.
  2. Close Heavy Background Tabs: Close resource-heavy tabs (YouTube, streaming audio, Discord) to prevent frame drops during Phase 2 Gaster Blaster salvos.
  3. Set Zoom Level to 100%: Browser zoom levels other than 100% can cause fractional pixel misalignment in HTML5 canvas rendering. Press Ctrl + 0 to reset.

#11 Frequently Asked Questions (FAQ)

What is Bad Time Simulator? +
Bad Time Simulator is a renowned HTML5 web simulator replicating the Sans boss fight from Toby Fox’s 2015 indie RPG Undertale (Genocide Route). Built by developer Jcw87 in Construct 2, it allows players worldwide to challenge Sans with authentic mechanics, customizable practice modes, and zero installation requirements.
Is Bad Time Simulator free to play online? +
Yes, Bad Time Simulator is 100% free and open to everyone on GitHub Pages. There are never any fees, downloads, paywalls, or registrations required to enjoy the full game.
How does Karmic Retribution (KR) damage work? +
Unlike normal RPG boss fights where getting hit gives you a moment of invulnerability (i-frames), Sans eliminates all i-frames. Every frame your soul touches a bone or blaster beam inflicts 1 HP direct damage plus toxic KR poison that drains your health bar continuously over time.
Can I play Bad Time Simulator on a school Chromebook or phone? +
Yes. The game runs smoothly on modern Chromebooks and desktop web browsers. Furthermore, our webpage includes built-in virtual touch controls (D-Pad and action buttons) for seamless play on smartphones and tablets.
How many turns are in the Bad Time Simulator boss fight? +
The encounter spans exactly 23 turns: Phase 1 consists of Turns 1 through 12, followed by the dialogue intermission trap. Phase 2 spans Turns 13 through 22, culminating in Turn 23 which is Sans' climactic 45-second "Special Attack."
What happens if you Spare Sans during Turn 12? +
If you spare Sans at the Turn 12 intermission, he instantly betrays you with his iconic "geeettttttt dunked on!!!" line, covering the entire screen in unavoidable bones for an instant Game Over. To proceed, you must choose ATTACK or heal with an ITEM.
Why does Bad Time Simulator run at 60 FPS instead of Undertale's 30 FPS? +
The original Undertale was built in GameMaker locked at 30 FPS. Construct 2 renders HTML5 games at the modern browser standard of 60 FPS. The projectile speeds and timers were mathematically scaled to match original timings while providing vastly smoother animation and sharper input responsiveness.
How do you avoid taking damage from Blue Bones? +
Blue bones only cause damage if your soul is actively moving while contacting them. When a cyan bone sweeps across your board, let go of all directional keys and stay completely still until it passes.
Can I practice individual attacks like the final attack? +
Yes! In the simulator's main menu, select "Single Attack" mode. From there, you can choose any attack from the entire 23-turn sequence (including the opening slam, platform runs, and the final laser wheel) to practice repeatedly with infinite lives.
Why is my keyboard not responding inside the game? +
Web browsers require the game iframe to be focused. Simply click anywhere inside the black battle screen with your mouse or tap it on mobile to pass keyboard focus directly to the game engine.

#12 Legal Attribution & Fair Use Notice

Bad Time Simulator is an independent, non-commercial fan-created tribute developed by Jcw87.

Undertale, its characters, dialogue, visual assets, and musical compositions (including "Megalovania" and "The Song That Might Play When You Fight Sans") are the intellectual property of Toby Fox. This web page operates under Fair Use guidelines for educational and simulation purposes. We enthusiastically encourage every player to support the official release of Undertale on Steam, Nintendo Switch, PlayStation, and Xbox.