Is there a reason why there is no such category? I would be interested in such a category with a friend...

It could be added in the misc categories -- there hasn't been any interest previously. I'm also not fully sure on what co-op runs entail, since i've never played co-op.

Are you looking to play all glitches, no OOB, or no major glitches?

We thought about running No Major Glitches, to get the best experience out of the game with no OOBs or any other big Glitches.

Also you asked what Co-Op Entails, its pretty much same as all Single-Player category just with a second controller/player. Player one is the host, and the second player is just a 'helper' he has to keep in Player 1s screen, they can't get out of the screen bounds, get too far away from each other.

A possible problem with this category is that in Hagers Cavern, the thief does not spawn because of a in-game bug. As the 2nd player doesnt TEHNICALLY have the mark the thief won't spawn which makes it impossible to beat one of the bosses, I think the only way to get to the boss in Co-Op is by Glitching through the door? Me and my friend will try to look deeper into that but I think there is no way to get him to spawn.

But what also could have a Sellsword Sub-Category, All Bosses. It would give be fun All Bosses, No Major Glitches, Co-Op. Not just rushing through the areas but also struggling to get the gear for it,and since its two players it would make it harder for both of them to have the right gear.

Also something should be done so that people dont just kill the Sellsword and then go off without him, cause that would make it like a SinglePlayer Category. A possible rule could be that everytime the Sellsword dies, you have to go back to revive him as soon as possible (go to a Sanctuary), no matter where you are you stop your current objective and go revive him (expect Boss Fights as you cant leave mid-fights).

To answer your question shortly, we thought about running Any% No Major Glitches and All Bosses No Major Glitches. If you have any more questions or such for the Co-Op in Salt and Sanctuary, to make a playable category and all, contact me on discord, SandWolfy#3463

No idea what you're on about with the thief, but the category is added. Only boss that isn't possible on co-op (without glitches) is the unspeakable deep, and that has nothing to do with any npc.