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DELTARUNE Fight Simulator

A free, fan-made battle simulator for DELTARUNE and UNDERTALE fights. It runs in your browser: no download, no account, no ads.

What it is

Pick a fight and play it. The battles are rebuilt one line at a time from the original games' battle code, so the attacks, the ACTs, the spells and the text work the way you remember. You can practise a single attack, replay a whole fight, or let the autoplay SOUL show you a clean run.

It is a fan project, made and maintained by one person. It is in beta, so expect a few bugs.

What is in it

Fights by chapter. More than 300 encounters: bosses and regular enemies from every DELTARUNE chapter, plus UNDERTALE fights.
Boss rush. Every boss of a chapter, back to back. There is also a gauntlet and a daily challenge.
Autoplay. A bot that dodges for you, to watch a pattern or learn a hard attack.
Replays, rewind and practice tools. Rewind a mistake, slow the game down, or drill one attack.
Bonus games. Dark World Survivors (a survival mode), Spell Card Rush (a bullet-hell boss rush), blackjack tables, MANIA (a rhythm game), Tetris (dodge falling blocks inside the battle box) and DARKDLE (a daily DELTARUNE guessing game).
Works on phones. Touch controls, a gamepad mode, and keyboard controls on a computer.

How to play

Open deltarunesim.com and press Z or Enter (or tap) on the title screen.
Choose a fight from the list. The tabs sort them by chapter; / searches.
In battle, Z confirms, X goes back, and the arrow keys move your SOUL. Dodge the attacks and win by fighting or by sparing.
Press Tab for the toolbox (practice, rewind, autoplay) and ? for every key.

Questions

Is it free?

Yes. It is free to play in your browser, with no download, no account and no ads. Any money in it is play money only.

Is this the official DELTARUNE game?

No. It is a fan-made project and it is not affiliated with or endorsed by Toby Fox. DELTARUNE and UNDERTALE are (c) Toby Fox. Buy the real games.

Does it work on a phone?

Yes. It has touch controls. Turn the phone sideways for the best view. On iPhone, Add to Home Screen gives you a full-screen app.

How do I report a bug?

Join the Discord at discord.gg/fWTAXYc4wR and post in the bug channel. Say which fight, what happened and what you expected. A screenshot or a replay helps a lot.

Disclaimer

DELTARUNE Fight Simulator is an unofficial, fan-made project. It is not affiliated with, endorsed by or connected to Toby Fox or the DELTARUNE team. DELTARUNE and UNDERTALE, their characters, music, sprites and text are (c) Toby Fox. Everything here is free, and any money in it is play money only. Made by puskevi. Follow @deltarunesim on X for updates.