Fantasy pins are generally designed by pin trading enthusiasts, whether individuals, groups or clubs. Disney "fantasy pins" are not sanctioned nor authorized by the Disney corporation, although many pins will have a "look" or theme that immediately reminds you of Disney or a Disney character. Designers have to be very careful not to infringe on copyrighted names, words and likenesses. As fantasy pins do not contain a Disney copyright, they CANNOT be traded with Disney Cast Members. However, they may be traded with fellow traders.
Since fantasy pins are typically manufactured in small numbers, many are touted as limited edition or LE pins. However, like any pin, it is entirely up to you to deem whether or not it is really a collectible or just another interesting pin to add to your collection.
Hope this helped some. Your pin pal...Disneyboy