Looks like I have a few bosses and mobs to kill for some of the skins, thanks as well on that list.
On random note, >.> angers me, but the Maliwan Elegance skin for Maya is glitched, the one I got from the Slag-Licked challenge is for Salvador. Seems Axton and Zero have the same issue from what I've read.
That's happened to me too, it's annoying. All challenge related skins should only be unlocked for the respective character your using ie: complete challenge as Axton you should get something for Axton not Salvador or anyone else.