The e-mail states that it is intended that it “for certain uses of a character, provides some additional compensation, above and beyond what you’ve already received.”
Basically if you’ve created a character for Marvel and he or she appears in a film/game/podcastcomic/whatever, you might get some extra cash.
Tell Marvel the character’s name and first appearance, and anyone else you worked with to create the character. And a Special Character Committee will decide if you’re eligible.
The you’ll have to sign another Special Character Agreement contract which will no doubt make sure that Marvel own that character in all it’s conceivable and indeed inconceivable forms. There are still a number of not-properly-contracted publishing deals dangling at Marvel, especially but not exclusively, post-bankruptcy when it seemed no one knew what the hell was going on. And there are films coming up, which may well have one or two contentiously non-contracted side characters appearances in them.
The recent Batman films saw DC Comics and Paul Levitz making ex-gratia payments to certain comics creators who created aspects that were used in the films. But Marvel seem to want to make this sort of thing official and put things on paper. Free money. Got to be a good thing.