Pokémon X and Pokémon Y

My sentiments too, though maybe not necessarily the dragon bit because Fairy type doesn't quite feel like an offensive advantage against dragon. Unless you want to pull in... fairy tails...

Hadriel

Exactly what I was thinking
Dragons are always slain in fairy tales


In regards to Fairy's weakness, if they really want to take it from Folklore:
Steel (Due to their weakness to Iron)
Poison (Due to their weakness to pollution)
Grass (due to their weakness to lemons ((yes this is a real thing)))
Ghost (with death being the opposite to life energy, I suppose)

earlier pokemon getting their types changed can be explained away too. Maybe a gateway to the area where fairy pokemon resided is torn open and fairy pokemon are discovered, through this they realize that pokemon like Clefairy (whose origins are unknown) and Togetic (who comes from a mirage dimension) are also technically classified as fairy type, similar to Magnemite and Magneton and how they were classified.