Deltarune Fight Simulator

A free fan-made battle simulator for DELTARUNE and UNDERTALE fights — 370+ encounters rebuilt line by line from the games' own battle code, so the attacks, ACTs, spells and text play the way you remember. Practice a single attack, replay a whole fight, or let the autoplay SOUL show you a clean run.

Playable below 370+ fights Chapters 1-5 + Undertale Boss rush + daily Works on phones

Free fan project — no download, no account, no ads. Keyboard, touch or gamepad.

Deltarune Fight Simulator

How to play

  1. 1
    Start the game

    Press Z or Enter (or tap) on the title screen.

  2. 2
    Pick a fight

    The list sorts encounters by chapter; press / to search. Every boss and regular enemy from DELTARUNE Chapters 1-5 is in, plus UNDERTALE fights.

  3. 3
    Fight or spare

    Z confirms, X goes back, arrow keys move your SOUL inside the bullet box. Win by fighting — or by acting and sparing, just like the real thing.

  4. 4
    Use the toolbox

    Tab opens practice tools — rewind a mistake, slow the game down, or drill one attack on a loop. ? lists every key.

What's inside

370+ fights

Bosses and regular encounters from every DELTARUNE chapter plus UNDERTALE — Jevil, Spamton NEO, Queen, GIGA Queen, Tenna, the Roaring Knight, the Titan, Undyne the Undying, Sans and more.

Boss rush

Every boss of a chapter back to back — plus a gauntlet mode and a daily challenge fight.

Autoplay SOUL

A bot that dodges for you — watch it no-hit a fight to learn a pattern you keep dying to.

Practice tools

Rewind a mistake, slow the fight down, drill one attack on repeat, or change the party and set your own stats and items.

Bonus games

Dark World Survivors, Spell Card Rush, blackjack tables, MANIA (rhythm), Tetris inside the battle box, and DARKDLE — a daily DELTARUNE guessing game.

Any device

Keyboard on desktop, touch controls on phones, and a gamepad mode — progress stays in your browser.

Controls

KeyAction
Z / EnterConfirm / FIGHT / ACT select
XBack / cancel
Arrow keysMove the SOUL / navigate menus
/Search the fight list
TabToolbox — practice, rewind, autoplay
?Full key list

FAQ

Is the Deltarune fight simulator free?

Yes — free to play in the browser with no download, no account and no ads. It's a one-person fan project and still in beta, so expect the occasional bug.

Is this the official DELTARUNE game?

No — it's a fan-made simulator and not affiliated with Toby Fox. DELTARUNE and UNDERTALE belong to their creator.

Which bosses are in it?

Over 370 encounters: every boss from DELTARUNE Chapters 1-5 including secret bosses like Jevil and Spamton NEO, plus UNDERTALE fights like Sans, Undyne the Undying, Omega Flowey and Asriel.

Can I practice one specific attack?

Yes — open the toolbox with Tab to loop a single attack, slow the fight down, or rewind to the turn you messed up.