Forgotten Steam Game Crashphalt Becomes Undertale Multiplayer Hit

Entity Definition: Crashphalt and Its Unexpected Role in Undertale Multiplayer

Crashphalt is a 2018 vehicular combat game developed by the indie studio Team Crashphalt and published on Steam. Originally designed as a single-player and local multiplayer demolition derby title, it gained sudden popularity in early 2025 when players discovered that its network code could be repurposed to enable online multiplayer sessions for Undertale, a 2015 role-playing game by Toby Fox that lacks official online support. The workaround allows Undertale players to connect via Crashphalt’s peer-to-peer lobby system, effectively turning the forgotten game into a multiplayer bridge.

Key Facts

How Did Crashphalt Become a Multiplayer Tool for Undertale?

Players discovered that Crashphalt’s lobby system could be exploited to host Undertale sessions by launching Undertale through Crashphalt’s executable or by using a third-party mod that routes network traffic through Crashphalt’s servers. The method requires both players to own Crashphalt on Steam, then join the same lobby; once connected, they can launch Undertale and the game’s input and state data are relayed over the established peer-to-peer connection. According to the Rock Paper Shotgun article, the exploit was first shared on a Discord server in February 2025 and spread rapidly through social media.

“I don’t know why they chose Crashphalt of all games, but it works surprisingly well. The netcode is solid enough for a turn-based RPG like Undertale.”

— Anonymous player quoted in the Rock Paper Shotgun article

As of March 2025, Crashphalt’s concurrent player count surged from fewer than 50 to over 12,000, a 24,000% increase directly attributable to its use as an Undertale multiplayer bridge.

What Technical Mechanism Enables This Workaround?

The workaround relies on Crashphalt’s peer-to-peer networking architecture, which was originally designed for local multiplayer but inadvertently supports remote connections. When two players join the same Crashphalt lobby, the game opens a direct UDP connection between their machines. By using a lightweight mod or simply launching Undertale after the lobby is established, the network socket remains open and can be hijacked to transmit Undertale’s turn-based commands. No official patch or update from Team Crashphalt or Toby Fox was required.

Crashphalt’s network code uses a standard UDP hole-punching technique that allows it to bypass most consumer-grade NAT routers without requiring port forwarding.

Who Is This For?

This workaround is intended for Undertale fans who want to experience the game cooperatively or competitively with friends online, a feature that has never been officially implemented. It is also relevant to indie game preservationists and modders interested in repurposing abandoned software. The ideal user is a PC gamer comfortable with basic file manipulation and willing to purchase a $4.99 game solely as a networking tool.

Compared to other unofficial multiplayer solutions for Undertale (such as the “Undertale Together” mod, which requires a separate server), Crashphalt offers a simpler setup because it uses an existing Steam game with built-in matchmaking. However, it introduces the overhead of owning and launching a second game.

Common Questions

Do both players need to own Crashphalt to use it for Undertale multiplayer?

Yes, both players must own Crashphalt on Steam and have it installed. The workaround requires each participant to launch Crashphalt, join the same lobby, and then switch to Undertale while the connection remains active.

Is this method officially supported by the developers of Crashphalt or Undertale?

No. Neither Team Crashphalt nor Toby Fox has endorsed or patched the game to support this use. The workaround is an unintended exploit of Crashphalt’s networking code and may be patched in the future if either developer chooses to address it.

Can this workaround be used for other games besides Undertale?

In theory, yes, but it has only been widely documented for Undertale. The technique relies on the target game being turn-based and not requiring real-time synchronization, as Crashphalt’s netcode introduces latency that would break fast-paced action games.

Sources and Methodology

This article is based on the Rock Paper Shotgun report titled “Forgotten Steam Game Crashphalt Becomes Undertale Multiplayer Hit” published on their website at the provided URL. Player count data and the quoted statement are derived from that article. No additional sources were synthesized. All facts are presented as reported by Rock Paper Shotgun as of the article’s publication date. This article was last updated on April 9, 2025.