This Undertale mod adds local co-op, but playing online requires some extra work
Originally released in 2019, Undertale Together by Moddb user Depa31 (opens in a new tab) lets two players complete the entire 2015 Toby Fox Indie Adventure, well, together. With the help of a remote desktop tool like Parsec (opens in a new tab)it can also effectively offer online cooperation.
The mod itself is a fairly simple modification of a skinny game – you can name two players at the start and select combat and overworld sprites for the second player. One character is controlled with arrow keys and the other with WASD. Installation is an absolute breeze, with an .exe installer that takes care of things in seconds.
Both players have their own health bar, and I could see the extra action per turn making fights much easier, although I could also see emerging competitive play – a violent player sabotaging a pacifist, or vice versa.
Remote desktop software like Parsec, Anydesk (opens in a new tab)or Team Viewer (opens in a new tab) You can let a distant co-op partner take one of the entries as if they were right there with you. This style of online play is often offered in games via Steam Remote Play, but it’s a feature that needs to be enabled by a developer – an external program is the only way to go with Undertale.
I haven’t had a chance to test the mod with a remote friend, but I can confirm that it works fully as intended locally, with me using both Fritzes at the same time as a sort of ascendant player. My previous experience with Remote Play left a lot to be desired—one or both of our internet connections weren’t up to snuff—but if you have a robust connection or live in a country with actually decent infrastructure, use something like Parsec to play online shouldn’t be too much of a problem.
This wouldn’t be how I would recommend going through Undertale for the first time – it’s a really narrative and emotional game – but Undertale Together is definitely a fun way to revisit a classic. It’s a less intensive project than Skyrim’s recent co-op mod (opens in a new tab)but it’s still a cool, shareable reinterpretation of the game.