Firstly, we'll be using Zandronum, a sourceport designed for multiplayer. If you have it already, make sure it is updated to version 3.2 and just download the core only link and overwrite files, otherwise get the full installer bundled with doomseeker.
https://zandronum.com/downloadYou will need doom2.wad, here is a link to it, just place doom2.wad in the same folder zandronum.exe is.
https://files.catbox.moe/tgzx7r.7zThe skin files we use allow us to play as Touhous. In your Zandronum install folder, make sure there is a folder called only "skins", if there isn't one then create it. Then place all the pk3 and wad files in the skins folder.
https://files.catbox.moe/rdcohm.7zThe WADs we're gonna use are contained in the following link. After installing Zandronum you should configure Doomseeker to have a separate WAD folder outside of appdata, as that is a bad location. Once you have set your WAD folder in Doomseeker place the following files there. If you are too lazy to do so you can just dump them where zandronum.exe is.
https://files.catbox.moe/6clg16.7zFinally, to configure your name and player skin, run zandronum.exe and go to player setup to change your name and skin.
As a final note, if any of the above links (except zandronum) don't work I've uploaded all of the above (except zandronum) into a single archive on Mega.
https://mega.nz/file/jF8wRDDQ#XgihmixE5H3yFgDM6__fjvWE6-eJJyqOlY43CRsT8eo