Ace Combat X: Skies of Deception is the first PlayStation Portable game in the Ace Combat series, followed by Ace Combat: Joint Assault. It used a modified version of the Ace Combat 04: Shattered Skies engine on PlayStation 2, and introduced new mechanics such as tuning aircraft parts as well as a gauge for certain things like enemy numbers.
Ace Combat X also expanded on the ability to choose alternate missions in some prior games. Players could choose which missions they want to go on next, or skip missions entirely. These decisions would change what enemies the player would face, and potentially increase the difficulty in the large climax missions.
Ace Combat X, like all other PSP games, could be converted to digital format in Japan for the PS Vita. However, as of 2016, this was no longer available. Players who already owned the digital version of Ace Combat X could still re-download it, but new players will not be able to acquire it.