(Disclaimer: I own this game on a different account.)
- Download the latest GZDoom for Linux and extract it into whatever folder you please.
- Download the Slooter and extract jotun.ipk3 into that folder.
- Run ./gzdoom
- Slootily sloot all the slooty sloots like a slooty slooter should.
- ???
- Profit.
Be aware it might not save to where you're expecting. (~/.config/gzdoom or somewhere like it.)