10 Obscure Comics Secrets That Took Years To Discover
7. The True Nature Of Spider-Man's Black Costume
Time To Discover: May '84 - Mar '88
Spider-Man was one of the superheroes who got involved (against his will) in the Secret Wars event, and while he was mucking about while wearing a torn and tattered costume, he discovered a strange ball of black good. When he touched it, it covered him and replaced his costume.
It was serendipitous, and despite the fact that Peter Parker is one of the most intelligent people in the Marvel Universe, he didn't really question it. Fast-forward from May to November of 1984 and Peter heads to Reed Richards for help in finally determining what it was.
Reed confirms that the costume is alive, and it's trying to bond with Peter permanently, so he helps him remove it, but the costume's true nature wasn't revealed for a little while after that.
Peter got rid of it and thought it was behind him, but the last time we see the Symbiote, it manifested into the shape of a man and swore revenge.
The Symbiote's true nature was finally revealed in the final pages of The Amazing Spider-Man #298 when he was introduced as having bonded with someone who also had reason to hate Peter Parker: Eddie Brock. The Symbiote had bonded to become Venom, and its true nature was finally revealed.