
ZEKE is mentioned in passing by Huey, but never actually seen.
Artifact Title: One of two Metal Gear games that do not feature some iteration of the eponymous Humongous Mecha - the Shagohod from Snake Eater was actually a competitor with the Metal Gear project. When the player contacts Miller while observing the logo of a mainline Metal Gear title, he will state the number of pixels or polygons that Snake's sprite or model was made of in that particular installment. Art Evolution: Commented in both Extra Ops. Reflex Mode and the corresponding differentiation between being Discovered and an Enemy Combat Alert note neutralizing all guards who Discovered you during the slowdown prevents an Enemy Combat Alert, which is what's actually counted against one's score are meant as one although being Discovered with Reflex Mode enabled does forfeit a No Reflex bonus, that's still better for one's score than the penalty from each Enemy Combat Alert. If (and more likely when) your chopper is spotted by the Marines when ex-filtrating after a mission, it doesn't count as an Enemy Combat Alert. The "Deja Vu" mission allows players to control low-polygon renditions of Solid Snake and the Cyborg Ninja from the first Metal Gear Solid in addition to the standard Snake, while "Jamais Vu" has players controlling the cyborg version of Raiden from Metal Gear Rising in one of three available color schemes (default, White and Inferno). And Your Reward Is Clothes: Both Extra Ops feature their own set of alternate skins that can only be used in those missions.
It states that given the size of the universe it is not improbable to assume that any number of branching timelines could exist at the same time, making it so that any given reality could be just as real as the other, simultaneously existing and not existing at the same time, existing in its own reality but not in that other reality.
Alternate Timeline: Discussed in the prologue description text for "Jamais Vu". Alternate Continuity: "Jamais Vu" is explicitly stated to have taken place in a different universe than the main game, which is obvious when you account for the sudden appearance of the Snatchers and the time-travelling cyborg.
It isn't essential to play Ground Zeroes to enjoy The Phantom Pain, but it serves to tease the main plot, allows players to get a feel for the darker tone, and as a refresher on the Big Boss timeline. The main story mission makes up 10 percent with the rest being divided among the side ops, extra ops, and trials. 100% Completion: Your completion ratio is given as a percentage at the title screen.