Plays inside your own copy of Ultrakill, on your device, not in a browser tab. Opens github.com in a new tab.
How to play
Have your own copy of ULTRAKILL installed: the mashup plays inside it.
There is no release yet: get its code from its repository on GitHub and build it as its README says.
Install it as its page says. What it asks for is just below, in the list's words.
Start the game the way its page says: some mashups come with a launcher of their own.
What it asks for
ULTRAKILL with BepInEx; put UltraDoom.dll in plugins and, in plugins/doom, a DOOM.WAD from a legitimate copy (shareware works), the RLNDGM.SF2 soundfont and (optionally) ultradoom.wad. The prebuilt DLL ships in the repository (no GitHub releases).