This is the Handbook guaranteed to make lawyers break out into a cold sweat. To qualify an entry has to have been in a licensed property published by Marvel but not actually part of the Marvel Multiverse. So all the characters from Marvel comics you enjoyed but wouldn't fit anywhere else.

The rules:
1. Any Marvel comic/magazine that fits the other parameters counts, even if Marvel isn't in the name. So Atlas, Timely, etc. Also any lines like Star, Epic, etc. But not Disney published titles as they're a separate publishing arm of the parent company.
2. Characters who only appear in adaptations of TV show episodes or movies or books are perfectly okay, as long they were not in the public domain at time of publication.
3. Crossovers neither count nor disqualify an entry. For example: Star Trek characters aren't allowed in through the crossover with X-Men, but their appearance in said crossover does not negate the Marvel-published Star Trek series of the 1970s.
4. Minor winks as the reader are okay as long as they don't prove a connection beyond a reasonable doubt. For example, in the Star Trek comic again there was a passing reference to Quincy Harker. That proves there's something there, but it's a bit hazy so it's fine. It could be that Harker is the only Marvel character in that Star Trek continuity. Rom however is disqualified because he undeniably interacted heavily with other Marvel characters for a time.
5. Characters created in a  licensed Marvel comic are fine, as long as Marvel doesn't own them. So RU Reddy doesn't count because Marvel owns him whether they want to or not. But everyone in Star Wars is owned by Lucasfilm, even if they were created for the comic, so they're okay.

So start torturing the lawyers!