Evil Libby is Libby's evil clone and Evil Sheen's girlfriend, who lives on Evil Earth. She looks and sounds exactly like Good Libby, but unlike Good Libby, she is the moral opposite of Good Libby: a very evil, sadistic girl and a total liar. She appeared in The Trouble with Clones when Evil Jimmy used a Dark Matter Power Chip to create a new Earth, where everyone is pure evil. She and Evil Cindy were giving a demonstration on wedgies and did a very painful atomic wedgie on Evil Nick. Then, the two decided to give a more painful wedgie on Jimmy with jumper cables. Just as they were about to tie him up, Jimmy defended himself and tied them up, painfully electrocuting them in the process. Later, after Jimmy undid the duplication process, Evil Jimmy sucked the whole Evil Earth into a void to prevent it from fading.

In the planned season four, Evil Libby and the rest of the clones would've escaped from the Dark Matter Dimension and attacked Jimmy and his class, who were on a field trip to an asteroid, provided by Jimmy himself.