Early this morning we got some details on and a trailer for the bonus mission that Xbox family editions of Ground Zeroes will include a bonus scenario set in in same location as the main game except you control Raiden in a fight again the body snatchers. Explanations for this inside.
In Kojima's latest move in his constant war against the suspension of disbelief, Raiden will time travel to the past to go into the Cuban base that is the setting for the MGS V prequel tutorial to deal with an influsx of body snatchers that are taking over the soldiers therein. By virtue of being a cyborg, Raiden is uniquely qualified to deal with this threat, and his cyborg vision allows him to easily identify who is still human and who isn't. The gameplay, then, revolves around dealing with the aliens while trying not to get the whole base down on you. It's essentially a "sneak around and kill specific targets mission," or so siliconera says.
This first part of Metal Gear Solid 5 hits on March 18.