The discovery of Crobat a few years ago by researchers in Johto is most remarkable for the fact that it took so long for them to be discovered. Zubat and Golbat have long been known to trainers across the pokemon world, largely as cave pests, but often as comrades as beloved as any Bulbasaur or Pikachu. And yet, despite the requirement for evolution simply being to make them happy, none of them ever evolved.
A Golbat's smile looks more like a painful grimace than a gesture of happiness, and this misunderstanding has stuck with trainers for millennia. It had therefore become a piece of accepted folk wisdom that Golbat hate the great outdoors and prefer their pokeballs and caves; in reality, the opposite is true, for Golbat's ancestors were pushed into caves by humans in the first place. Likewise, Golbat were thought to be unable to digest poffins, and were thought of as too ugly for contests; in reality, they love their taste and enjoy contests as much as battles. So accepted was this belief that when Crobat were finally discovered, it was by accident, when a Golbat was left outside in an open-air enclosure with a pile of poffins nearby.
A great deal is still not known about Crobat, including the long-term health effects of this evolution; indeed, some suspect that poffins are bad for them after all. What they are notable for is restlessness. A Crobat's wings are so big that they can barely stand, nor are they effective enough to glide; instead, they are flapped constantly, with the pokemon never seeming to tire or stop, only to hover with seemingly more effort than it takes to move. But they are almost always smiling, and their smile looks like happiness.