One of the oft-forgotten (possibly intentionally forgotten) facts about Howard the Duck is that he is technically a Marvel Comics character. It was always my understanding that he was only a parallel universe character.
His bio on Marvel's website, however is a bit unclear. It makes mention of teaming up with She-Hulk and staying with Generation X for a time, but does not specify which reality any of those events occurred in. It also specifically mentions Counter-Earth.
Is there any canon instance of Howard the Duck ever crossing over into Earth-616?