Uncanny Valley/Fan Works

• In With Strings Attached, Brox looks and acts like a normal little child—until he/she starts acting his/her real age. Her/his whole mien shifts, which creeps out the four considerably.
• Nebiros in New Dawn is already an outlandish looking demonic clown, barely even human looking, so it might count as an aversion, as he does not look human enough to qualify for the trope. However, it is played straight with his speaking patterns. He talks as a whole like a young teenager, has no sense of personal space, views reality as a game and is oh so enthusiastic in a very child-like way about what he does. And, suffice to say, he does not see anything wrong with being a serial killer: "Because its so fun, watching em flail about like a fishy!"
• In X-Men fanfic Mutatis Mutandis, Northstar is basically described as vampirically beautiful. Rogue notices when she stares at Northstar's face for more than a few minutes, he looks so eerily perfect that he seems creepy and surreal.