It's Fun to play with, that's for sure, but I would have preffered if you couldn't spam them as you want and not available by all other Civ of the same SS.
A good approach to implementing fantasy stuff, is to add more realism to them. As an examlpe, you could only Train Vampires in a City that's adjacent to some specific kind of Mountain (have no Idea what that could be, that's just to limit things), and for a limited number.
If you have watched "Carnival Row" (a Fantasy Series), then you would agree that the showrunners/producers/writers did a really good job by making the Events play in a Rennaissance/Industrial era where Fantasy Creatures are treaded with racist prejudice und only tolerated because they do the dirty Jobs for them. The show is really realistically made, with Political intrigues and a Postwar Scenario. Sometimes you could even forget that it's a Fantasy Show, but a show based on historical events.
(Tbh I didn't thought that the show would break the Fantasy Glasses you put on when watching Fantasy, but this one did, at least for me. A LOTR made realistically like that show, with events based on real history (implemented history, I know that LOTR is based on WWII), would be an ALL-Time #1 hit)
That to say, a good Lie that even you believe, can be considered as the Truth.