Nigon is the second underground race.

Of course, the Nighon race should be included. The more castles, the more fun it is to fight. Personally, I don't know why the developers put the Elves underground; they should be in the forest, and your castle should definitely be underground...
Also, where did you get the idea that Ifrit is male? It's a spirit, and spirits are genderless (and besides, Ifrit is a fire demon, so it's not a spirit). And by "monster," do you mean Behemoth? It's a servant of the Devil, so it doesn't really fit the Dungeon theme. Maybe it would be better to include some kind of dragon (azure or rusty), but otherwise, I like everything. Moloch.