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.
(..) Then the longer we have before the projections catch us? Exactly. - My subconscious seems polite enough. - Ha, ha. You wait, they'll turn ugly. No one likes to feel someone else messing around in their mind. Cobb can't build anymore, can he? I don't know if he can't, but he won't. (..)2010 Inception