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.
(..) Hands up. l know this music. Let's change the beat. l think we're being attacked. They're everywhere. They're warriors, and they're ugly. They got big teeth, big foreheads, big ears, and they stink. Mangalores. The government sent me to help you. (..)1997 The Fifth Element
(..) What did she say? She knows exactly where they are. My dear Aknot, how about those two planes you borrowed? ls that you? What an ugly face! lt doesn't suit you. Take it off. That's better. Never be ashamed of who you are. You're warriors. (..)1997 The Fifth Element