Disgaea: Hour of Darkness/Bonus Worlds

A number of extra regions can be opened via proposal in the Dark Assembly. In order to do so you must have unlocked the proposal, have the proper amount of Mana available, and have enough influence with the Assembly (or be able to grind them beneath your boot-heel).

Prinny Land
Mana: 400

Area Map: Prinny Land 1, Prinny Land 2, Prinny Land 3

Cave of Ordeal
Mana: 700

Area Map: Cave of Ordeal 1, Cave of Ordeal 2, Cave of Ordeal 3 (one of the best spots for lvling), Cave of Ordeal 4, Cave of Ordeal 5 (make sure that you can reach the zombie king by having a character that can throw 6 squares away or you'll never be able to finish this map), Demon Hall Mirror (I think it's only availible in the ds version and the psp version)

Human World
Mana: 1200

Area Map: Central City, Neo Eden, EDF Headquarters(dont forget to steal the astro suit before killing General Carter)

Alternate Netherworld
Mana: 3000

Area Map: Alternate Netherworld, Hall of Sin, Hall of Penance, Malefic Seal, Warrior Maiden(Priere "Roasted Pork!")

The Mysterious Seal
Mana: 5000 Influence: 5000