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.
(..) is going to swim up and bite your culo? ( woman screams ) It's just a sand tiger shark. Pretty ugly, but harmless unless you're a fish about that big. I heard it scared that girl so bad, she ran all the way up (..)2002 Shark Attack 3: Megalodon