My reactions to those 3 (they seem legit)
Volcanion: Looks like he can seriously burn/flood his enemies
Diancie: we have a rock/fairy already and you look like it if it evolved
Hoopla: I feel like Egyptians are going to takes offence the second they see you
Theory time
http://i.imgur.com/4BZMyLz.jpg Volcanion is in Jaune Plaza
I will go do some special hunting around there to see if I find anything
Hoopla is waiting for the one
Remember the hex girl that says "no your not the one". Hoopla is psychic/ghost aka the 2 types Hex npcs use. Maybe you need to bring her an item. (Someone visit her with the strange souvenire just in case)
Diancie is a hidden evolution
It has a VERY similiar body design to another rock/fairy which I have caught. (Need to catch a new one since I gave it up to wonder trade)