The Proudclad 2 has a weakness, it turns out. Toward the end, it doesn't recover, so keep hitting it. You do have to stay alive, though ;-) After that, it's on to Chapter 13, and a somewhat unexpected chance to level up for awhile before taking on the final bosses. You come upon a couple of warp portals, and you can drop back down to Gran Pulse for awhile and look around for chocobos or whatnot. Or go back to Edenhall. The portals are two-way affairs, so there's no reason not to. Barthandelus III will keep for a bit, or even, considering the downbeat ending if you've been reading ahead, maybe for months.