If Y developed a character which is substantially similar to X's character and did so with knowledge of X's character, it is likely that Y's work will be found to be infringing of X's rights. It is possible, therefore, that Y could have her own, equally-valid copyright in her character, if she came up with the character without knowledge of X's. Back to TOP 3. Yes, if handled properly. Briefly, that section provides a defense to a claim of infringement when the defendant makes use of protected material for the purposes of criticism, commentary, and certain educational uses.
Parody is considered a form of criticism or commentary.
However, the Fair Use defense is narrowly defined. Of course, a parody is not subject to these limitations if it is done with the authorization of the copyright owner. Back to TOP 4. Generally, the accrual date is considered to be the date the plaintiff knew, or reasonably should have known, of the infringement. At least in theory, a character, if it reaches the level of specificity necessary to gain copyright protection, should thereafter be protected in all media, regardless of whether it has been exploited there.