The only thing to note about the rest of this dungeon is that there are four 'dead end' rooms with minibosses. You only need to visit the third one to get a key item; the others are purely optional (but give you a fistful of rare gems, so they're worth visiting if you need to power up some weapons still).
Halfway through you'll also confront Flotsam again, though he's pretty easy to beat. Be sure to snap a photo of him, as it's required for the last two inventions.
Watch Dark Cloud 2: Flotsam Revived! (And last two inventions) from spoonshiro on www.twitch.tv
And as a big throwback to the first game, our secret optional uberboss is the fake Dark Genie from the first Dark Cloud! He's... not particularly tough. If you're inclined for some reason, you can snap photos of him and the Zelmite rocks for a couple of extra photo points (though this is rather pointless, since the game ends immediately after you defeat him).
Watch Dark Cloud 2 Part 12 (Finale) from spoonshiro on www.twitch.tv