Outside of gengar in gen4 i can't actually think of another occasion when you could encounter a special evolution like this in the wild until gen 8.
Admittedly I did stop playing after my x/y save with all my pokemon all the way back from ruby got deleted so I may not remember, or may have missed some but i don't think I've ever really encountered it. And if I did, I was so young that I don't remember!
It's like learning that waterfall or headbutt were gen 1 attacks.
by Paks-of-Three-Firs