Daylight Glint

Darklight Spark is a clone of Princess Twilight created by Dr. Nefarious to be the leader of the bearers of his Elements of Disharmony. Being infused with power from Discord, Darklight represents Magic, and is very evil, knowing everything about evil under the influence of corruption. She has no cutie mark since she was freshly born.

History
Dr. Nefarious was able to obtain Twilight's DNA, and use it to make a clone. The clone was the toughest one to corrupt due to having Twilight's knowledge of friendship and skills, but she was eventually, she became corrupt by being infused with power from Discord. She was the most powerful of the Elements, and knew evil better than Dr. Nefarious. But she didn't wish to become an ultimate evil, but wanted to instead be a low threat, indicating that she is still good inside.