The Rainbow of Darkness is a powerful dark magic once possessed by Tirek, master of Midnight Castle. Tirek used it primarily to effect evil transformations upon other beings, such as turning Scorpan into a gargoyle, various animals into his guards and Stratadons, and ponies into dragons. His ultimate goal was to employ it from his Chariot of Midnight to bring eternal night to Ponyland. However, his plan was thwarted when his rainbow was countered by the Rainbow of Light, which reversed the Rainbow of Darkness' effects and destroyed both it and its master.