From Wikipedia:
Dissidia: Final Fantasy (ディシディア ファイナルファンタジー Dishidia Fainaru Fantajī) is an action RPG/fighting game developed and published by Square Enix for the PlayStation Portable as part of the campaign of the Final Fantasy series 20th anniversary. Information on the game was first released during the "Square Enix Party" event of May 2008. The game features characters from different Final Fantasy games and centers around a great conflict between the heroes and villains, as the god of discord, Chaos, tries to wrest control of their worlds from the forces of good.
Dissidia: Final Fantasy's genre has been described as "dramatic progressive action" and its graphics are in three dimensions. It has wireless one-on-one multiplayer and fights revolving around the use of individual special skills of characters to do damage to opponents. Players can also customize their characters with equipment.
Character movement is fully functional within the three-dimensional field map. Characters are able to perform special maneuvers using the environment by pressing the Triangle button, similar in function to the Reaction Command feature of Kingdom Hearts II. Traps with a variety of ill effects can be found throughout the arena.