Main offense: The moustache
What went wrong: Nosepass was a sort of clever idea for a Pokemon, because it looks like one of the impressive stone statues from Easter Island. Its evolution, however, was totally unnecessary. Probopass looks more or less the same as Nosepass, just bigger and with the addition of an unfortunate moustache. All we can really say is: Why?
Lesson learned: Adding a moustache usually makes something worse, not better.