My ASL Dictionary has a Witch showing the ASL hand sign for UGLY. For the sign for Extremely Ugly (almost frighteningly horrid), I went with a creature a little less human, but still cute and adorable.
A cartoon of a Green Forest Troll with a grimace on his face shows the ASL hand sign for HIDEOUS. The index fingers of the “ONE” hands are crossed in front of the nose to draw apart and bent into X hands, like a double version of the UGLY hand sign.