I'm curious what an All Bosses run would look like, since the category heading is here on the site. Does anyone have a demonstration video, or even a more detailed description? I'm assuming it would start like an Any% run by running past Briar to enable the swapper. Then you go around and defeat all the bosses. Do you have to defeat Briar last?

I would say you are correct. Get the swap broom first then defeat all of the other bosses in the quickest order. And yeah, you would have to defeat Briar, either saving it for last or beating it first after getting the swap broom.

I think I know where the All Bosses category idea came from:

http://speeddemosarchive.com/Anodyne.html#SSAllBosses