ShadowQuilava

I've used one in Sun and Moon.....it's alright, but it only really works in its School Form, but this is Rejuvenation, it's much harder

I know it had to be pushed back between the Reborn Ep17 beta and the public release, so it must still be viable in these games.

Possibly, but I guess it can only be good in these games when it has a move to counter it's weaknesses, like Ice Beam, but as we know, the good TMs won't appear till late game.