WMG / Resident Evil 0

Billy knows more than what he told Rebecca
What happened to Billy Coen in Africa (interestingly enough, people think the protagonist in RE5 is Billy, though clearly it's Chris, now having seen the new trailer), and what did it have to do with the mother virus? (I initially thought that Billy's exclamation in the factory was simply an RE2-style plot dodge; it's assumed that the player knows what a given virus is by now, if only from files, so the character does too. However, Billy says "mother virus," and no file in RE0 mentions that. They're all about the Progenitor.)
  • Could possibly tie in with Billy's time in Africa. Why else would the US government get involved in a crapsack country's little civil war? (Be honest, seriously.)
    • Honest? OIL.
      • That's if they are in, oh, Nigeria. We only know they are in Africa. There are so many ways to get rich in Africa, for all we know, they could be in there for the tusks, damn it.
      • If there are loads of ways to get rich in Africa, THEN WHY THE HELL IS EVERY SINGLE COUNTRY DIRT-POOR RIGHT NOW?!?
      • Because of the people getting rich off of taking their resources. Dur-hey.

Wesker and Birkin just pretended to be rivals in order to prevent Marcus from getting suspicious and/or paranoid about them.
One of the diaries in Resi 0 notes that the two are very competitive, yet they seem to be perfectly willing to cooperate in containing the T-virus outbreak during the game itself, and Birkin's letter to Wesker at the end of REmake is pretty friendly. Since they apparently also cooperated on Marcus's assassination, it's apparent they intended to usurp his position from the beginning, and pretended to be rivals to prevent the idea from ever entering his mind.
  • I don't think they ever had to. The diary just said that Marcus wanted them to be rivals and that the Assistant Director (or whoever the fuck that was) should try to get on that shit, but it never said anything about it actually working. I mean, they might be competitive, but considering that Wesker didn't snap Birkin in half at some point, it was probably more of a friendly rivalry than anything else.

Umbrella builds many of its laboratories in the same style.
It would explain why Rebecca and Billy can visit an area that looks like the entrance of Birkin's lab in Resident Evil 0.
  • That is the entrance to Birkin's lab.
    • Yet it's just thrown in at last moment as a reference to RE 2, and the game was originally meant to go from Marcus's lab straight to the Water Treatment Plant. Given that it's a last minute thing with not much thought behind it, it also doesn't add up with the geography. The part with Birkin's lab in RE 0 is basically a non-canon easter egg.
  • Though that would explain why the Foyer in Marcus's headquarters looks nearly identical to the foyer of the original Mansion.
  • Pretty much confirmed in the files of R Emake. Spencer hired Trevor to create the Mansion, and probably the style used inspired all the other facilities.

Rebecca reunited with Billy sometime after the Raccoon City incident.
  • ...and settled down with him. It may be the reason neither of them has been seen, or heard from since.

The Leeches are actually the ones in control of Marcus
  • Take a look at his face when he transforms into the leech queen. He is taken by surprise mid-laugh, throws up and has a look of shock on his face while he transforms. There are actually two minds; Marcus's mind, and the leech hive mind that allows him to exist. He thinks he is in control but they can take over at any time.