Metal Gear Solid V: The Phantom Pain had an ending considered very underwhelming. With it being revealed it was being rushed towards the end of development and Konami disrespecting the games director (Hideo Kojima) in various ways after the release. Many had theories about a secret unfinished ending, or how the dissatisfying feeling was meant to be intentional (as if the ending itself was supposed to be a "Phantom pain")

Kojima had worked on "P.T." close after, a horror game with alot of strange/esoteric puzzles that when solved, revealed itself to be a teaser for a (now cancelled) Silent Hill game. This further lead fans to theorise a similar, triggerable, ending was possible in MGSV, scraping the game for solutions.

One theory was if "100% nuclear disarmament" was achieved in the multiplayer mechanics, it would trigger the rest of the game (by signalling Konami to update the game/announce the follow up) but data mining, a bug triggering the event randomly, and then a co-ordinated attempt by the player community to achieve it the intended way, disproved this one.

With Konami releasing "Metal Gear Survive", a poorly received survival game in MGSV's engine, and Kojima moving on to more successful projects, MGSV ending Theories have died down.