This is a topic that was already well-covered in The Physics of Superheroes. But while The Atom and Ant-Man/Giant-Man/Too-Many-Names-Man have size changing as their explicit super power, a lot of anime (and near-anime) characters do it incidentally, as a part of other transformations. Of course, so does the Hulk.
For example, Devilman is considerably taller as the demon Amon than as the human Akira. (Or in Mazinger Z vs. Devilman, much taller.) Well, at least he’s supernatural.