(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.)

On dolphin I have found the bug still works, and I've found that, using it, you can enter the Cellar without needing to get the key from Ethon. I don't think it's faster, because talking to Ethon doesn't take that long, but it shows that this bug could have applications.

If you create a second player while running into the wall behind Bartley, that player can run on top of the walls into the back room, and activate the transition into the basement.

I do have an actual copy, but I need time to set it up. Haven't used my PS2 in years

I'll test on dolphin in the meantime though, planning on experimenting more tomorrow

{Disclaimer, I'm using a PS2 emulator. There's a chance this bug won't work on console}

I'm still experimenting with this bug, and as of right now I haven't found anything useful to do while OOB, but I figured I'd post about it in case anyone else had some insight.

Where I was performing this bug: Just after the first of the three gates in Sewers 2

I would run into to wall beside the open gate (as if trying to run into the save point) and add a second character. The Character (I was using Elf) would appear on top of the map.

Then, if you jump and, at the peak of your jump, move Up (in the direction of the door) you can clip back onto the roof proper.(note: It's a very precise angle you have to hit. If you it it off you will either end up back in the room (on top of P1 basically) or near the save point.) Once there you can move around, but (at least, as far as I could tell) cannot get back in bounds.

If, once OOB, you use P1 to recall, then once back at the tavern, Go to character select and remove P1 (making the elf P1), and then attempt to Recall. The recall should fail, and then once you enter a load zone (Either Baldur's Gate or The Cellar) you will be OOB (and unable to see yourself)

When OOB movement is finicky, and there are many dead zones where if you touch them you will become unable to move. As of right now I cannot find a way to get back in bounds.