an 'ugly duckling' that has become a beautiful swan [=an ugly/unsuccessful person or thing that has become beautiful/successful]
('informal') That dog of yours is '(as) ugly as sin'. [=very ugly]
The house is an 'ugly duckling', but it has a lot of potential.
(..) Get everyone ready. Now! Where is the baby? You lost it? Sid! It's so ugly. But it's adorable. Hello, pumpkin. Where did you find it? The poor kid all alone in the wild. Sabers gang nailed on it. So I just snatch it. So brave. (..)2002 Ice Age