Short answers, pulled from the story.
Dissidia 012 Final Fantasy is a fighting game developed and published by Square Enix for the PlayStation Portable. It was released worldwide in March 2011 and serves as both a prequel and a remake of Dissidia Final Fantasy.
Dissidia 012 Final Fantasy features thirty-one playable characters in total. Nine characters were new to the game, with six available from the start including Lightning, Vaan, Laguna Loire, Yuna, Kain Highwind, and Tifa Lockhart.
Dissidia 012 added the Assist system, which lets players summon an ally into battle to attack or defend. Three countering mechanics, Assist Breaks, EX Breaks, and EX Revenge, were also introduced or significantly revised to balance the EX Mode that players found too powerful in the first game.
Dissidia 012 sold 286,117 units in Japan in its first week, topping the Media Create charts. Its predecessor sold close to 500,000 units in its first week on the 18th of December, 2008, making the original's launch significantly stronger.
Takeharu Ishimoto composed the score for Dissidia 012 Final Fantasy. The American band Kidneythieves sang the second part of Feral Chaos's boss theme, "God in Fire", after Ishimoto wrote the song and requested their collaboration.
Famitsu scored Dissidia 012 Final Fantasy 38 out of 40, with four reviewers awarding individual scores of 10, 9, 10, and 9. That total was two points higher than the score Famitsu gave the original Dissidia Final Fantasy.