Stage 6 - Here we fight Adell from Disgaea 2. Too bad that he and all the other cameo characters for that matter have no English voice overs :(
The fight is not too hard. You can abuse the extra 3 attacks while he keeps using skills.
Stage 7 - Now you have to fight both Adell and Rozalin, also from Disgaea 2. Rozalin is 500 levels stronger then Adell, has a Legendary Nemesis (one of the strongest monster weapons in the game), and the Geo Symbols. Rozalin can pretty easily take out your characters with her AoE attacks, and if she doesn't then Adell finishes them off. Before I could tackle this stage I had to grind A LOT. Laharl is level 5000 and I did some stuff you'll see in future videos before coming back here.
Steal the Nemesis to reduce Rosalin's damage, don't put two characters next to each other to avoid the AoE. Once you beat them they'll join your party!
Stage 8 - The last stage is a reward for all the hard work up to this point. It's the best grinding spot in the game. Very similar to CoO3, but the enemies give even more exp and the bonus exp effect is higher.
00:00 - Demonhall Mirror 6
07:59 - Demonhall Mirror 7
27:45 - Demonhall Mirror 8