Alien robotic units have gained an increase in effectiveness, as well as introduction of two new units:.It is required for some of the newly introduced XCOM transhuman technologies. These nanites are each made up of organic and mechanical components. Meld is a suspension made up of billions of cybernetic nanomachines. XCOM operatives will be forced to advance swiftly in order to secure Meld canisters with delay-activated self-destruct systems some of the aliens' more sophisticated cybernetic units such as Mechtoids also grant Meld when killed. A new resource, called 'Meld', is introduced.Similar to the numerous expansions of the Civilization series, the pack retains the core storyline but adds a broad variety of content. The player manages the XCOM headquarters in almost real time progress, but much of the gameplay consists of turn-based battles against the invading aliens and some with the rogue human faction EXALT across the globe. The gameplay and plot of XCOM: Enemy Within largely remains the same as XCOM: Enemy Unknown with some additional features. The PlayStation Vita version is only available bundled with Enemy Unknown under the title, XCOM: Enemy Unknown Plus. The iOS and Android versions were released as stand-alone apps not requiring the original mobile port of Enemy Unknown to play.

The Windows, OS X and Linux editions require XCOM: Enemy Unknown to play Enemy Within was released for Xbox 360 and PlayStation 3 as part of the Commander Edition bundle with Enemy Unknown. On March 22, 2016, the game was released on the PlayStation Store for PlayStation Vita. The game also came to the iOS App Store and Google Play Store a year after the initial release, on November 12, 2014. In June 2014, Feral released both XCOM: Enemy Within and its base game XCOM: Enemy Unknown for Linux. XCOM: Enemy Within was released for Microsoft Windows, PlayStation 3, and Xbox 360 in November 2013. The expansion pack primarily adds new gameplay elements to the base game, as well as introducing new themes of transhumanism via aggressive gene therapy. XCOM: Enemy Within is an expansion pack for the turn-based tactical video game XCOM: Enemy Unknown.

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