My Theory for the Horsemen of Apocalypse

Mister Sinister is easy to explain, just have a sequence at the beginning where Scott is in the planecrash, he wakes up and finds the his mutant power has manifest and Nathaniel Essex comes and gives him ruby quartz glasses to help him control. Nathaniel can be like he is in the comics, an 18th century man given mutant powers to serve Apocalypse.

Oh of course it can be explained, but both Essex and Shaw are really old dudes, both from the Victorian era, it is implied in First Class that Shaw is really old, he could have been following Apocalypse his whole life.
Honestly I just think it would be cool to see Kevin Bacon back, and think it would work for the story. Have Apocalypse resurrect Shaw as Mr Sinister then have Sinister find Cyclops. I understand your reluctance to the idea of merging the two characters though.

Could always bring Azazel, Emma Frost, Riptide and Angel S from the dead as the Horsemen.

Remember, Singer does not read (or care about) the comics, so just because it happened it the comics does not mean anything. Although, you have some good ideas there.

I think Scott is a great choice. I agree with Cherry, it all depends on which time line or period they use. Most likely Wolverine or Sabertooth for Death, unless FOX pics up a book a goes with Angel.

Funny side note: My oldest daughter has been watching the Ultimate Spider-Man and now loves DeadPool. She asked me if he's ever been in a movie. At this point I explained Wolverine: Origins to her. She went and looked it up and watched it and had one comment. "Did the people that made this movie ever read a comicbook?" From the mouth of a kid ladies and gentleman. That's why I don't pay to see FOX-Men movies anymore.

Sorry, got that backwards, Polaris was Pestilence and Sunfire was Famine.

I had thought that about Apocalypse and his horsemen BEFORE I read the comics - I think a lot of people took to the video game as their entry point, or maybe that was just me. At any rate, once I picked up the Fall of Mutants issues and that more recent one after M-Day, I saw that things were quite different.

Gambit and Angel were both the Horsemen of Death. They didn't have the ability to make people die instantaneously, and only Angel really symbolized death (considering he was both suicidal due to having his wings amputated and believed dead in a plane crash at the time)... in fact, the only real "augmentation" lied within their appearances.

In both stories, some random guys were picked for War, and they had no connection with any other X-Men or mutant for that matter, having only appeared to be abducted. Again, Fall of Mutants was a bit more symbolical - the veteran (I don't even think he was a mutant) was paralyzed and kept alive by machines, feeling isolated and abandoned. Apocalypse gave him full mobility, and powers just like Arclight in 'the Last Stand'. Post M-Day, some depowered mutant astronaut goes to the moon to die, and gets abducted, thrown into a chamber with some other guy, and basically the one who kills the other was to become War, but Apocalypse's servant did the dirty work for him. He just had power weapons, and had his body bulked up.

Pestilence BEGAN with an augmentation of plague powers - a random Morlock named "Plague" was picked to have her powers enhanced. She's exclusive to the Fall of Mutants. Post M-Day, it was Polaris, and she was having a serious mental breakdown as a result of the stress the use of her powers had caused her mind overtime. I guess in that way, she was harming herself, but her abilities are the same as Magneto's. When she's kidnapped, Apocalypse makes her a carrier of every airborne pathogen, and threatens to release her on the United Nations.

Famine was pretty obvious in Fall of Mutants, just like Pestilence. She was a mutant who had problems with her powers, was anorexic, and dissolved organic matter. After Apocalypse gets done with her, she makes everyone she targets waste away in the most ridiculous way possible. After M-Day, Sunfire (who had his legs chopped off by Deathstrike) is given prosthetic limbs, and his fire powers have an added effect of making people think they are starving (a signal to the brain produced in his light bursts that affects the body).

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I had an idea that's not possible now about incorporating the Horsemen into events triggered by servants (both willingly and indirectly) of Apocalypse, with the help of Sinister. Sinister would have been the shapeshifting bad guy who puts everyone against each other, and convinces Trask to weaponize the Sentinels.

On that front, Sinister would pose as Trask and program/install an EMP in every Sentinel.

WAR!
The Sentinels would openly attack mutants, leading to some pacifists to lash out. The X-Men in particular would be divided, as some would take human hostages in order to guarantee their safety, on top of defending themselves. The Sentinels would eventually catch up with the X-Men, bombing the mansion, and forcing them into their secret tunnels. Literally operating underground, the X-Men would find the Morlocks - an entire society of mutants who had been living in hiding years beforehand.

PESTILENCE!
The mutant cure has been delivered to bottling companies, and dumped into the water supply in certain populated areas. While not as potent as the injected payload, the chemical agent has greatly diminished mutant abilities. Many X-Men are overwhelmed while trying to prevent this from continuing, captured, and put into special prison camps.

FAMINE!
In order to level the playing field somewhat, Sinister detonates the Sentinels across the globe - triggering an electronic apocalypse, crippling humans and mutants alike. In the most populated cities, everything with an electronic circuit has been fried, and civilization panics.

DEATH!
Cyclops (accompanied by Sinister) approaches the X-Men, resurrected, and heralds the return of Apocalypse. He orders that they give themselves up, abandon their hope of coexisting, and join the new world order of survival of the fittest. They can leave their lives behind and rise from the ashes of this doomed society as conquerors, or they can perish in the wake of Apocalypse.

Roll credits.

@TheMexicanSuperman
is that confirmed anywhere? even so, if it is announced that the characters will be in Apoc, that doesn't mean they will be good guys. right?