(Note; this bug requires two controllers, and I was testing on Dolphin. Would be good to have someone test this on console, at least until I can get mine set up)

Ok so I found a way to skip the bugbear chieftain fight. I haven't done a run doing this (because I've been bug hunting this game like a madman) so I don't know if not talking to Ethon after the fight will be harmful. But, assuming that it isn't, here's how you can skip this boss fight.

So once you walk into the room with the boss, you need to stand here. (excuse the bow, I was cheating for equipment so that I could get there quickly for taking pictures, though I have done this without any cheats and it still works)

Then, you need to create a second player, I use the elf just because she's the fastest. Once she's created, it should look like this.

Then (and this is the hard part) you need to jump with the elf, and at the peak of her jump move her towards the Weapon rack. If done properly, she'll appear in the room, and she can activate the stairs down.

If it doesn't work, and she ends up either further on the roof or in the boss room, just delete her and try again. I've been practicing with this a lot though, and I find it to be a very consistent bug, once you get the hang of it.

Once through the stairs, just delete player 2 and go through the next level the same as always (haven't found a way to skip the three gates yet, but I think I'm getting close.)

Holy smokes, I've been sick for a while, but I'm really sorry I didn't see your posts!! This is interesting stuff, amazing work Tsumo!!