I'm working on creating a Mega-Lucario centered team and Aerodactyl is in it - however, I need its hidden ability, but since it's a fossil, I can't get it. Is there any way for me to get Aerodactyl's hidden ability, and if so, how?
However Dream World is now unavailable
The only other way would be to trade. Or ask for one.
There is the DB Chat and multiple Trading Forums such as Reddit and GameFAQs
There is not a way to get an Aerodactyl with Unnerve in Gen VI, and its also no longer available in Gen V because their Dream World is shut down. So your best shot is GTS or hooking up with some hackers for your game. Good luck!