DELTARUNE FIGHT SIMULATOR

Every boss from DELTARUNE Chapters 1 to 5 and UNDERTALE, rebuilt from the games' own battle code. Free in your browser.

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No account, no ads, nothing to buy. Fan-made, not affiliated with Toby Fox.

  • 361fights to pick from
  • 1-5DELTARUNE chapters, plus UNDERTALE
  • 7bonus games
  • $0no ads, no account

THE TRAILER

Seventy seconds of what is in here: every boss, any mistake undone, your own ideas, and a SOUL that plays by itself.

EVERY CHAPTER

Pick a fight from the list and play it. The attacks, ACTs, spells and lines behave the way they do in the games, because they come from the games' own battle code.

Browse the fight pages or open the full list of 361 fights

MORE THAN FIGHTS

  • The fight list in the simulator, with the boss filter on.

    BOSS RUSH

    Line bosses up back to back, play a draft run that deals you four bosses and a perk between each, or take on today's daily fight.

  • The Attack Lab: one attack from the Titan fight, its damage, turn length and seed.

    PRACTICE AND REWIND

    Practise one attack on a loop, slow the game down, or rewind a mistake and try that turn again, then watch the replay.

  • The autoplay SOUL dodging an attack on its own.

    AUTOPLAY

    Turn on the autoplay SOUL and watch it dodge a whole fight without a hit. Handy when one attack has you stuck.

  • The Roaring Knight fight in the simulator.

    CUSTOM PARTIES

    Change the party, set your own stats and items, and take that team into any boss.

BONUS GAMES

Seven extra games made from the same parts: survive a horde, graze a spell card, play a rhythm chart, guess the daily fight and more.

THE DESKTOP APP

The same game as a Windows app. It downloads everything once, keeps itself up to date, and plays offline.

GET THE APP
The desktop app's main screen: the logo over Cyber City and a PLAY button.

JOIN IN

Bug reports, ideas and new fights are talked about on the Discord. Updates go out on X and TikTok first.

FIGHT STATS

Every finished fight adds one anonymous row. The totals are public.

See all the numbers