I don't watch the Anime so I was kinda waiting for someone else to get it =p
All three of them were part Ghost type, but that's not specific to the Anime hint.
Aight, aight, since no one could solve it, I'll just clarify it myself. Yes, they're all Ghost-types, and all of them were owned by Jessie of Team Rocket.
As for your new riddle, all three of them have Hisuian forms in Legends!
Now, for a new one: Kecleon, Greninja, Cinderace. Hint: ability.