Hidden Evil

Those...THINGS over there...No, don't look! They'll see you! OK, can you see them now? Well the thing about them is that they are EVIL. Of course they don't look evil, you think they wanna let everybody find out? But they can't fool me. I know them for what they truly are. But nobody would just believe me because they are...


 * a kitten - Cats Are Mean
 * a bird - Feathered Fiend, Owl Be Damned, Morally-Ambiguous Ducktorate
 * a bunny - Killer Rabbit, Hair-Raising Hare
 * a toy - Creepy Doll, Demonic Dummy, Sealed Evil in a Teddy Bear
 * a harmless object - Happy Fun Ball
 * a normal person - The Mole, Affably Evil
 * a Nice Guy - Bitch in Sheep's Clothing
 * a loser - From Nobody to Nightmare
 * the Harmless Villain - Not-So-Harmless Villain
 * The Woobie - Woobie, Destroyer of Worlds
 * cute and innocent - Cute and Psycho
 * beautiful - Evil Is Sexy
 * seemingly a woman - Villainous Crossdresser
 * an Old Friend - Big Bad Friend
 * the love interest - Yandere, The Vamp
 * the Sidekick - Poisonous Friend
 * the mentor - Evil Mentor, Sensei for Scoundrels, Treacherous Advisor
 * the trusted advisor - Treacherous Advisor, Evil Chancellor
 * royalty - Fake King, God Save Us From the Queen, The Evil Prince
 * on your team - Token Evil Teammate, The Mole
 * New teammate - Sixth Ranger Traitor
 * my dad - Archnemesis Dad
 * my mom - Evil Matriarch
 * my adopted mom - Wicked Stepmother
 * my wife - Black Widow
 * someone else's wife - Lady Macbeth
 * my husband - The Bluebeard
 * me - Evil Twin, Enemy Within, Enemy Without, Super-Powered Evil Side
 * a child - Enfant Terrible
 * dead - The Undead
 * not even born yet - Fetus Terrible
 * on the side of Light - Light Is Not Good, Knight Templar
 * from the Church - Corrupt Church, Path of Inspiration, Sinister Minister
 * a clown - Monster Clown
 * a doctor - Deadly Doctor
 * a dentist - Depraved Dentist
 * a scientist - Mad Scientist
 * a teacher - Evil Teacher
 * a policeman - Corrupt Cop, Dirty Cop, Rogue Cop, Police Brutality
 * a nun - Nuns Are Spooky, Nun-Too-Holy
 * Santa - Bad Santa
 * an angel - Fallen Angel
 * God - God Is Evil
 * named harmlessly - Super Fun Happy Thing of Doom, Fluffy the Terrible
 * pure of heart - Pure Is Not Good
 * that random unremarkable guy on the corner - They Look Just Like Everyone Else
 * a celebrity, businessperson, politician or other public figure - Villain with Good Publicity

Watch out for anyone with free will, and any new science or media (old or new) as well.

See also Dark World, Mirror World and the Masquerade for when whole worlds of evil are hidden from you. Hidden Villain for the trope about these guys hiding.