Grotesque: The Nature of Transformations

We have creatures, so with creatures come transformations. What are those like?

• Some arguments for keeping them rather pretty, even when people hulk out: the side-plots are meant to be YA-style, and those keep the love interests attractive as necessary
• Arguments for going a bit scary: we don't have to look at them, it's cooler and feels more realistic, the people involved wouldn't care because it's what they're used to

Vampires transform? I vote no. Better if they have to conceal features like exceptionally pale skin and pointy fangs, that it's just how they look.
Werewolves? Yes, but not fully into a wolf. Human-sized furry monster person. Possibly a few who are more fluffy than monstrous.
I can't think of anyone else...Mermaids. They should shift significantly between surface look and underwater look. Make 'em creepy, with greenish skin and pointy teeth and webbed hands and just go full fish.