Letter: X X: Beyond the FrontierX: TensionX2: The ThreatX3: ReunionX3: Terran ConflictX4: FoundationsXargonX-COM: ApocalypseX-COM: Chimera SquadX-COM: Terror from the DeepX-COM: UFO Defense (UFO: Enemy Unknown)X-COM 2X-COM 2: War of the ChosenX-Morph: DefenseXenonXenon 2: MegablastXixit