Episode 51: Kingdom of the Flies

Kingdom of the Flies, also known as Episode 51 and the Phantom Episode, is a mission that was not included in the released version of Metal Gear Solid V: The Phantom Pain due to time constraints. Footage of incomplete cutscenes and concept art for this mission are shown in a bonus Blu-ray disc included with the Collector's Edition of the game. The mission would've involved Snake pursuing Eli and the other child soldiers in Central Africa after they hijacked Sahelanthropus from Mother Base, a plot thread that was left unresolved in the finished game.

The released game has some leftover code referencing this mission, most notably the mention of a "FLYK" as a location in the game, as Episode 51 would've been set in an island outside the Angola-Zaire Border Region that all the other missions set in Central Africa took place in.

Speculation

 * While "Kingdom of the Flies" is referred to as "Episode 51" on the collector's disc, there is evidence within the game's data suggesting that it was actually supposed to occur before the events of Episode 43 (Shining Lights, Even in Death) since the sole mission set in FLYK has the code number 10230, while Episode 43 is 10240.
 * During the interview at Gamescom 2014 Hideo Kojima had mentioned that he was always energized by the "making of" documentaries of movies that didn't "go that well through development", showing how everyone on the team was working really hard.