Main offense: Looks like a cross between a dirty snowball and an evil cat head
What went wrong: This is just an all around ugly, dumb-looking Pokemon. From its oversized teeth and generally creepy face to its dirty snowball body, there's nothing appealing here. We know that not all Pokemon can be cute and cuddly like Mew or Pachirisu, but it's not just that it's ugly - it's that it doesn't even have anything to show for its hideousness. Pokemon like Venusaur or Abomasnow might be just as ugly, but they also look intimidating as hell. Glalie, on the other hand, is just kind of floating there looking, well, ugly.
Lesson learned: If you're going to make a Pokemon look that ugly, it better be ferocious-looking to compensate.