pitch document for BioShock, which was planned to be a very different monster from the game we all know and love. Specifically, a sea monster.
Some things in the document stayed true -- genetic modification was a major aspect of the pitch. Most of it ... well, let's just say we're glad things changed the way they did. We're not sure the story of Carlos Cuello, who must infiltrate a remote island run by cultists to rescue a wealthy heiress, would be quite so memorable. Also, those aforementioned genetic modifications give you traits of different sea creatures instead of regular ol' superpowers.
Also, there was supposed to be multiplayer. Multiplayer! In BioShock! Have you ever heard of anything so preposterous?