X-Dimension

The X-Dimension is a series of Maps in Disgaea 3: Absence of Justice and Disgaea 4: A Promise Unforgotten. Like the Dark World in Disgaea 2: Cursed Memories each X-Dimension map is an altered version of one of the main story maps, making the map significantly harder. It is done by adding in powerful Enemies and having difficult Geo Puzzles. Some Geo Block effects can in fact be devastatingly fatal consequences (such as draining a large amount of HP from a character or even causing an Instant Game Over). Some maps even have turn limits, meaning the player only has so many turns before an event occurs that prevents the map from being completed or causing the previously mentioned Instant Game Over. An extremely common Geo Effect that is only found here is known as Absolute Area, which prevents players from entering the affected area, prevents players from lifting or throwing any character or Geo Block standing on it, and causes the Geo Block generating the effect as well as the characters on them to be invincible.

Disgaea 3: Absence of Justice
To access the X-Dimension, players need to encounter and defeat an Item World Pirate. Defeating the Pirate nets the player an Illegal Ticket which gives players access to a X-Dimension Map. Illegal Tickets can also be bought from a Reaper in the Item World. He has 2 different sets of purchasable Tickets, and the set he has out depends on how deep the player is in the Item World. There is one Reaper that sells the first set on Floors 1-49 and another that sells the second set on Floors 51-99. Once a player has acquired at least one ticket, they can then unlock a bill that lets them get the Tora no Ana Club. Placing a character in the club unlocks a Female Samurai in the Evil Academy Campus Hub Area and lets you access the X-Dimension.

Disgaea 4: A Promise Unforgotten
Illegal tickets (now called Promotionhell Tickets) can only be bought from a Mystic Beast in the Item World. Like in Disgaea 3, there are two sets of tickets which can be bought, depending how how deep the player is into the Item World. There is one scalper who sells the first set on Floors 1-49 and another that sells the other set on Floors 51-99. Unlike Disgaea 3, however, buying just one ticket is enough for the Magic Knight who grants access to the X-Dimension to appear in the Base. Pirates in Disgaea 4 do not yield any Illegal Tickets as the two Scalpers sell all Illegal Tickets for each X-Dimension Map now. In A Promise Revisited, the game's Vita Port, the shop is no longer split, and all 63 Tickets may be purchased from the same scalper.

Prizes
In both games, clearing a certain number of X-Dimension Maps allows you to acquire items from the X-Dimension Gatekeeper as you progress. In Disgaea 3, clearing 25 allows you to access the Land of Carnage, and in Disgaea 4, completing around 40% of the X-Dimension is one of the requirements to access the Land of Carnage.

Trivia

 * In Disgaea 3, all X-Dimension Maps have the song Great Gilder as background music, while in Disgaea 4, it is the song Black Gate.
 * In the remakes of Phantom Brave, the Merchant of Death comments that main antagonist Sulphur comes from the X-Dimension.