Dark Cloud/Muska Lacka

Sun & Moon Temple
When you and Theo arrive at the temple you here a voice warning you not to go in. It's one of the Sand Warriors, guardians of the nearby village of Muska Lacka, you can change his name from the default, Ungaga, now. Muska Lacka was destryed by the Dark Genie and the warrior is so distraght over failing in his duty that he just sits there being depressed. Theo stays behind to try to get warrior back into fighting shape while you go on to explore the temple. When you go inside there is a kind of lobby area; go down the steps to the back and enter the temple proper. In the future, you can skip the lobby by selecting Sun & Moon Temple (inside) from the map.

Sun & Moon Temple (inside)
This dungeon doesn't have any odd quirks about getting to the next level or to the back area. King's Slate opens the next level, Stone Key opens doors within a level, and Secret Path Key opens back levels. The enemies here start fairly easy but get harder (of course). Bomber Head starting in level 3 explodes as it dies, so you may want to use Xaio or Ruby on it.

At level 4 there is a dialog between Theo and Ungaga. Theo tries to use you as an example of how a warrior should really act, but Ungaga doesn't listen.

Level 5 is a Goro only level, but if you've been leveling his weapons with the others this shouldn't be a problem. At level 7 there is another dialog between Theo and Ungaga. Ungaga reveals he was trying to protect Mikala, his fiancee, but failed. Theo tells him that Mikala was saved and they see a shooting star as a good omen.

In level 9 there is a set battle between Gol and Sil, two golems. Even in close quarters these shouldn't pose much of a problem since they move so slowly. The way out is blocked until Ungaga joins your party.

Ungaga
After completing level 8 you should have the components needed to complete The 3 Sisters' House. Do so and watch the cutscene; Ungaga is now in your party and Theo goes home to Brownboo. There doesn't seem to be any weapons available for Ungaga now.

Sun & Moon Temple (inside, cont.)
Enter level 9, fight the monsters there if you haven't already, and use Ungaga's charged attack to blow away the dark barrier that blocks the way to the next level. Similar barriers will appear randomly in dungeons from this point on. As with other newly introduced characters, you get an Ungaga only level soon after this. The bad news is that you can't buy a weapon for him yet as with Ruby so you're back to same problem you had with Xiao and Goro. But you do get three levels to possibly get treasure with a weapon for Ungaga before you get to his level, which is better than the two levels you got with the others. Also, the enemies on Ungaga's level aren't particularly difficult so you may get by with his Fighting Stick and some extra Repair Powders. In the later levels you run into Steel Giants, these are similar to the Golems you encountered earlier in the dungeon but have higher HP and are much tougher on weapons, so you'll probably want to bring a few extra Repair Powders for them. Continue on through level 17.