Moonbow Jounce

Gray Dash is a clone of Rainbow Dash created by Dr. Nefarious to wield the power of his Elements of Disharmony, in which he will represent the element of Disloyalty. Since she was created with the harnessed power from Discord, she is Rainbow Dash's mental opposite, being unloyal to anyone except Nefarious, and will refuse to listen to anyone who stands in his way. She has no cutie mark since she was born.

History
Gray Dash was created after Dr. Nefarious obtained Rainbow Dash's DNA. After 2 days inside a cloning chamber, Gray Dash was born the same age as Rainbow Dash, but with no cutie mark. But before she could bare the Elements of Disharmony, she needed to obtain the potential. Using a machine fueled by some of Discord's magic, Gray Dash became Rainbow Dash's mental opposite, being defiant, brash, and arrogant. But side effects of this change in personality is that Gray will show signs of positive thinking and feelings. It is also indicated that there is signs of good in Gray because he prefers to become a lesser threat than a huge threat, and wants to conquor Equestria with her clone friends and without Nefarious.