With the release of the Afterbirth expansion, there was a new secret, but this one was not so easily discovered. However, dataminers quickly discovered his existence by looking at the game code and he became common knowledge within a few days, to the disappointment of the game creators. When The Binding of Isaac: Rebirth released last year, a super-secret character called The Lost was included, with a complex unlocking mechanism that was designed to be a community scavenger hunt. Since the ARG seems to be officially over and Ed's post-mortem will be coming soon, it seems my work here is done.
There are a couple other writeups out there, by KevCar518, piraka12, and PC Gamer, but I wanted to make one of my own so I could keep it updated as new information surfaced. Here I'm going to try to document as thoroughly as possible what exactly happened, from the release of Afterbirth to the addition of the Keeper. Though the ARG has only recently concluded (assuming it has in fact been completed!), many people have been asking for more info on what's been going on.
