No, they haven't. It's the strangest thing, really --- it seems as though no one's ever seen them before, either.

Granted, we did have something like this back in April, as well... it was some sort of slug, then. Really rather messy things... I wasn't terribly sad to see them go, but everyone went wild about them because of how unusual it was to see a completely new Pokemon.

They're apparently native to some other region and are actually called Goomy, but until we were made aware of that everyone decided to call them Bloobers.