Zandronum

My mod for Doom 2, Bring Your Own Class, is something I've tried to load, MULTIPLE times. But unfortunately, Drag and Drop refuses to work. I use portable core version.
Are the sourceport and core different things? Is BYOC just uncompatible with the core version?

Try running it from the command line using "-file yourmodhere.pk3".

Alternatively, you can use Doomseeker's "Create Game" menu, set everything up as if you were gonna host a server, and then click "Play Offline".

Alternatively alternatively, you can use a launcher. I use Rocket Launcher by Hypnotoad. It's old but it works great and it supports drag+drop as well as a "favorites" list so you can quickly add your most preferred mods.