Giganticus Pain-in-the-butticus took about 45 minutes and 4 tries, but once we figured out the best way to avoid his attacks (mostly with me running in, tapping him, and running away like a frightened child), it worked.
Then, the final boss was ridiculously easy (as we know):
Ironically, the first half of the dungeon was way easier than before, but I think that's largely because we knew what to expect.
Apologies for the images slipping off the side; that'll be fixed when we change to the new layout, which I'll be working on again.