Fairweather Skip

Cruelshy is a clone of Fluttershy created by Dr. Nefarious in order to serve as one of the bearers of his Elements of Disharmony. Using harnessed power from Discord, Cruelshy was meant to be Fluttershy's mental opposite. Cruelshy is mean, cruel, and not afraid to lash out at anyone she hates. She lacks a cutie mark due to being freshly born.

History
Obtaining Fluttershy's DNA, Dr. Nefarious was able to create a clone at the same maturity. But while the clone was successfully created, she had the same personality but no cutie mark. So Dr. Nefarious used a machine fueled by harnessed magic from Discord, and reversed her personality, making her cruel and mean. Being Fluttershy's mental opposite, Cruelshy didn't prefer being with Dr. Nefarious, and instead wanted to be less of a threat, indicating that some good still remains in her.