An unofficial Undertale multiplayer workaround has turned free 2018 platform fighter Crashphalt into a strange Steam success story, sending players and reviews toward a forgotten indie game because it supports Remote Play.
Image: steamcommunity.com
A forgotten Steam fighter became Undertale’s unlikely online co-op helper
Crashphalt, a free Steam game released in 2018, has suddenly become useful to a crowd that mostly is not there to play Crashphalt. According to PC Gamer, the neglected indie game saw a freak 1700 percent jump in player activity after players began using it as part of an unofficial setup for the Undertale Together mod. That is the concrete oddity at the center of the story: an eight-year-old competitive platformer is now being downloaded, reviewed, and name-checked because it helps players push Toby Fox’s Undertale into online multiplayer territory.
The discovery came from RetroSpecter, who posted on Reddit that they released Crashphalt as their first Steam game and only occasionally checked its Steam page afterward. The developer wrote that the game had roughly 10 reviews when it launched, but recently had over 500, with many of those reviews making Undertale jokes rather than discussing Crashphalt itself. Kotaku, citing Steam review history, put the pattern more sharply: between Crashphalt’s October 2018 release and December 2022, it had 20 reviews, while from January 2023 onward it gained 552 more. Rock Paper Shotgun’s snapshot listed 555 total user reviews at the time of writing. The exact counts vary by outlet and timing, but the same picture emerges across the sources: Crashphalt’s Steam page was overtaken by Undertale players years after its original release.
RetroSpecter’s own reaction was less corporate crisis meeting than indie-dev bewilderment. In the Reddit post, they summed up the moment of recognition with, “Okay yeah I like Undertale too but Wtf is going on?” The answer was not a streamer wave, a sale, or a patch. It was a mod community discovering a loophole.
How Undertale Together works, and where the online workaround begins
The Undertale Together mod, credited in the source material to Depa and hosted on ModDB, is a co-op mod for Undertale. The confirmed point that matters for players is that Undertale Together adds local co-op. Rock Paper Shotgun also reports that it includes co-op-specific battle mechanics and puzzles. By itself, though, it does not normally provide online play.
That distinction explains the whole Crashphalt detour. Local co-op means two people can play together on the same machine. Online co-op means Steam needs some way to stream that local session to another player, and Undertale does not normally support Steam Remote Play. According to VGC, players found tutorials explaining that a game with Remote Play support could be used as a bridge: download a Remote Play-enabled game, move or copy relevant files into the Undertale install folder, then activate Remote Play through that setup. Rock Paper Shotgun describes the specific workaround circulating in the community as dragging Crashphalt files into Undertale and renaming the Undertale executable.
That is the practical answer for anyone searching how Undertale Together works: the mod itself is a local Undertale co-op mod, while the widely discussed online method is an unofficial Steam Remote Play workaround. The sources do not describe this as official support from Toby Fox, Valve, or the Crashphalt developer. It is a community hack built around Steam’s Remote Play behavior and a free game that happens to have the right flag enabled.
Why Crashphalt became the chosen game
Crashphalt was not selected because its mechanics secretly resemble Undertale. It was selected, as far as the developer can tell, because it met a mundane technical requirement. RetroSpecter wrote that the only requirement for the workaround was that the chosen game have Remote Play enabled, adding that Crashphalt being free likely helped. “I dunno why they chose Crashphalt,” the developer said on Reddit. “But I imagine there are tons of games that fit that bill. Crashphalt was just the lucky game chosen for the honor.”
That accidental role is why the Crashphalt Steam page now reads oddly if you arrive expecting a normal user-review record. VGC reports that the game had over 500 Steam reviews and an “overwhelmingly positive” label, with most of the recent reviews referencing Undertale rather than Crashphalt. RetroSpecter’s Reddit post described the review status as “mostly positive,” while other outlets describe the current page as “overwhelmingly positive.” That is less a factual contradiction than a reminder that Steam review labels and totals can shift, especially when a small free game is hit by a sudden influx of joke reviews and mod-adjacent downloads.
The funny part, and the faintly brutal part, is that Crashphalt itself is a real game with a clear design hook. RetroSpecter described it as a local multiplayer platform fighter in the vein of TowerFall and Samurai Gunn. VGC describes a four-player competitive platformer where players use a ground pound to create shockwaves in the terrain and knock opponents off the stage. Rock Paper Shotgun similarly describes players sending out seismic ripples to punt each other off-screen. That sounds like exactly the sort of small, readable couch battler that can live or die on whether anyone gathers around it. Instead, Crashphalt found a second life as plumbing for someone else’s co-op dream.
The developer is surprisingly fine with being mod infrastructure
This could have been an ugly story about a small developer watching their first Steam project become a punchline. Some of the reviews, according to Rock Paper Shotgun, either ignore Crashphalt or mock it while praising the Undertale use case. Kotaku points to Steam reviews that asked whether the developer was bothered that people cared about the game mainly as a tool for modding another game.
RetroSpecter’s answer was measured and generous. In the Reddit post, the developer said they do not mind what Crashphalt has become, explaining that they have moved on to other projects and think it is “really cool” that the game found a second life. They also tied that reaction back to Undertale’s influence, writing that Undertale came out around the time they were getting into game development and was “incredibly inspiring” to them.
There is one important caveat in RetroSpecter’s blessing. The developer wrote, “So as long as Steam doesn’t take any issue with how Crashphalt is being used, have fun playing fighting Sans with your friends.” That sentence keeps the confirmed facts in their proper box. RetroSpecter is not objecting. The mod community is clearly using Crashphalt. But the setup remains unofficial, and none of the provided sources say Valve has approved this specific use of Remote Play or that Undertale’s developer has endorsed it.
A review surge is not the same as a rediscovery, but it can still help
The strangest tension here is that Crashphalt’s Steam success signal now points in two directions. On paper, more than 500 reviews and a highly positive rating suggest a late-life discovery. In practice, many of those reviews are apparently artifacts of an Undertale multiplayer mod pipeline. That makes the Steam page less reliable as a measure of Crashphalt’s quality than it would be for a game whose new reviews came from people actually playing it as intended.
Still, indie games often survive through accidents of visibility. RetroSpecter wrote that Crashphalt helped them learn development from start to finish, helped them make friends they still keep up with and work with, and became one of the stepping stones toward working on games full time. The current spike does not rewrite the game’s original reception, but it does put a name, a developer, and a quirky local fighter back in front of players who might otherwise never have seen it.
There is already a path from curiosity to support. In the r/IndieDev thread, RetroSpecter pointed interested players toward their current project, Draftula, on Steam. That is a useful reminder of how attention travels in indie spaces. Someone arrives for an Undertale co-op mod, laughs at the weird Steam review archaeology, and may end up wishlisting the developer’s next project. Even if only a fraction of the new visitors actually try Crashphalt, that is still a better fate than having a clever little platform fighter sit unseen in the depths of Steam.
Practical guidance for players curious about the Undertale co-op mod
If you are here because you searched for an Undertale multiplayer mod or an Undertale co-op mod, the cleanest confirmed answer is this: Undertale Together is designed around local co-op, and the online method involving Crashphalt is a community workaround using Steam Remote Play. The sources describe Crashphalt as useful because it is free on Steam and supports Remote Play, not because the Crashphalt developer built anything specifically for Undertale.
That also means players should treat the workaround with the caution any unofficial mod setup deserves. Back up saves before changing game folders. Follow current instructions from the mod’s own page or active community posts rather than old reposted guides. Understand that moving files between game folders and renaming executables can break after Steam, game, or mod updates. If you want a straightforward supported experience, the sources do not establish that Undertale has official online co-op.
For Crashphalt itself, the pitch is simple and refreshingly physical: it is a free local multiplayer platform fighter built around ground pounds and shockwaves. If the Undertale Together mod sends you to its Steam page, consider giving the actual game a look before treating it as a disposable launcher trick. It may have become famous for the wrong reason, but small games have lived on thinner miracles than that.