7. Howard The Duck
Howard the Duck is a satyrical Marvel character who regularly parodies conventional comic book stories. Since he's been a burlesque director, a wrestler, a video store clerk, a martial artist and a wizard, it's clear Howard is not supposed to be taken seriously. Because he's so unconventional, this avian superhero rarely associates with Marvel's major players and many of his stories aren't considered canon.
Still, Marvel shouldn't be afraid to embrace the character more. Weird characters like Rocket Raccoon and Groot prove that ANY superhero can work if they are incorporated into a story correctly. Other satirical heroes like Deadpool and Spider-Ham have recently become mainstream, so why is Howard not given a chance?
He mightn't work alongside Thor or Iron Man, but he should fit in just fine with other eccentric heroes like the Guardians of the Galaxy or even Doctor Strange.
Speaking of which, Howard teamed up with Sorcerer Supreme during the Empirakul storyline a few years ago and gelled really well with the other characters. Since Howard has been around for decades, it's clear he has a devoted fanbase, so Marvel shouldn't be afraid to implement him into more significant storylines.