An Undertale multiplayer mod turned a forgotten Steam game into an unlikely hit

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A few months ago, indie developer RetroSpecter noticed something unusual about Crashphalt , their first completed game that launched on Steam in 2018: Since their last check-in on the neglected platformer, Crashphalt had suddenly gained over 500 reviews. In its first four years, it had barely managed a dozen.

And almost none of those new reviewers had anything to say about Crashphalt itself. Mostly, they just talked about Undertale.

(Image credit: Cold Pressed Games) "Does ANYONE want to play Undertale with me???" one reviewer writes. Another calls Crashphalt the "best game to never actually play." Others insist that "Undertale is a pretty cool game."

"Okay yeah I like Undertale too," RetroSpecter wrote in a Reddit thread recounting their discovery, "but wtf is going on?"

Crashphalt owed its unexpected renaissance, they soon realized, to Undertale Together , a fan-made Undertale multiplayer mod that, typically, only supports local co-op—a limitation that players found a clever way to circumvent.

(Image credit: tobyfox) If you look at Crashphalt's SteamDB charts , you'll notice that between November and December 2022 its peak daily player count jumped from 6 to 107—a roughly 1683% increase. That timeframe happens to coincide with the December 2, 2022 upload date of a certain YouTube video —one that RetroSpecter would eventually come to understand as the source of that sudden spike in player activity.

The video outlines a method for playing Undertale Together online by copying Crashphalt install files into a modded Undertale directory. Afterwards, renaming the Undertale executable to "Crashphalt.exe" is all it takes for Steam to believe it's RetroSpecter's platformer and allow Remote Play multiplayer for what would otherwise be a local-only mod.

And yes, it works for Deltarune, too. Unsurprisingly, there was another spike in Crashphalt player activity in June 2025, coinciding with Deltarune's full paid launch on Steam. Why the video's creator chose Crashphalt specifically, however, is still something of a mystery.

(Image credit: Cold Pressed Games) "The only requirement for the hack is that [it] has Remote Play enabled, and I guess it does help that Crashphalt is free. But I imagine there are tons of games that fit that bill," RetroSpecter said. "Crashphalt was just the lucky game chosen for the honor."

While all those players might not technically be showing up for Crashphalt itself, RetroSpecter says it's "really cool to see that the game has found a second life"—even if it's an unconventional one.

"Undertale came out around the same time I was getting into game dev, and was incredibly inspiring to me," the developer said. "So I think it's really cool that it's found a way to impact the community even if in a small way and act as a way for friends to play the game together."

It's a refreshingly generous response to what's easy to imagine as an irritation—though RetroSpecter did leave a slightly self-interested postscript addressed to Undertale's own developer:

"Toby Fox. If you read this, let me know if you... like… wanna make a game together. Thanks."

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