Bad Time Simulator (Sans Fight)

Bad Time Simulator (Sans Fight) is a fan-made Undertale battle simulator that recreates the famous Sans encounter as a challenging browser game. Control your heart-shaped soul, dodge fast attack patterns, manage your health and items, and learn each sequence until you can survive the full fight.

• Fan-made recreation of the Sans battle from Undertale
• Fast bullet-hell style dodging
• Multiple soul movement mechanics
• Normal, Practice, Endless, and Single Attack modes
• Custom Attack support in compatible versions
• Fixed attack patterns that reward memorization and practice
• FIGHT, ACT, ITEM, and MERCY battle commands
• Healing items for managing health during longer attempts
• Retro pixel-art presentation inspired by Undertale
• Play instantly in your browser with no download required

• Normal Mode – Take on the complete Sans fight with attacks appearing in their normal sequence.
• Practice Mode – Practice difficult sections with less pressure and continue working on patterns that give you trouble.
• Endless Mode – Face a continuous series of attacks and see how long you can survive.
• Single Attack – Select individual attack patterns and repeat them until you learn how to avoid them consistently.
• Custom Attack – Load or test custom attack sequences in versions that support the feature.

During Sans' turn, you control a small heart inside the battle box and must avoid incoming attack patterns. Once the attack ends, you can choose an action from the familiar Undertale battle menu.

Battle commands include:

• FIGHT – Continue your attempt to defeat Sans.
• ACT – Check or interact with your opponent.
• ITEM – Use available items to recover health.
• MERCY – Access the mercy option during battle.

Success depends heavily on recognizing patterns, making precise movements, and knowing when to use your limited recovery items.

Different parts of the fight change how your soul moves.

• Red Soul – Move freely in all four directions inside the battle box.
• Blue Soul – Gravity affects your soul, turning movement into more of a jumping and platforming challenge.

Attack sequences can also combine changing gravity, moving platforms, bones, blaster attacks, and rapidly changing battle-box layouts.

Bad Time Simulator is designed around repeated attempts rather than traditional upgrades. Each run helps you learn the fixed attack sequences and become more consistent.

Progress can include:

• Reaching later parts of Normal Mode
• Memorizing attack patterns
• Practicing individual attacks
• Improving movement accuracy
• Learning Blue Soul sections
• Managing health more effectively
• Surviving longer in Endless Mode
• Completing the full Sans fight
• Attempting cleaner runs
• Creating or loading custom attacks on supported versions

The more familiar you become with each sequence, the more manageable the full battle becomes.

#### Desktop

• Arrow Keys or WASD — Move your soul
• Z or Enter — Confirm or select
• X — Cancel or go back
• Arrow Keys — Navigate the battle menu

The controls stay simple, but different soul modes can change how movement behaves during attacks.

Bad Time Simulator (Sans Fight) is a browser-based Undertale fangame created by Jcw87 that focuses entirely on mastering one challenging boss encounter. Learn fixed attack patterns, practice difficult sections, manage your items, and keep retrying until you can survive the complete fight. With Normal, Practice, Endless, Single Attack, and Custom Attack options, it gives players multiple ways to learn and replay the Sans battle.