The Dark Spark is the very spark of the God of Destruction, Unicron. It is the antithesis to the Matrix of Leadership, where the Matrix grants wisdom, the Dark Spark empowers its master to bend the very fabric of the universe and its inhabitants to his will. It can also corrupt an Equine's heart with Unicron's evil. It can also bring out an Equine's dark side. Megatron used the Dark Spark in Oz to turn it's inhabitants to puppets. Optimus Prime and Megatron engaged in a beam lock between the Matrix and the Dark Spark. The Matrix's beam overpowered the Dark Spark's beam and was blasted out of Megatron's chest and the Dark Spark was ejected into space and landed in Equestria. It also has the ability to travel through universes.
Twilight Sparkle, Rainbow Dash, Pinkie Pie, Rarity, Applejack, and Fluttershy found the Dark Spark buried in a cave and it corrupts their hearts with Unicron's evil and Twilight puts the Dark Spark on chains and puts it around her neck proclaiming herself to