Sometimes ponies just have a bad day. They spill their cereal, trip in the mud, have their checks bounce, and get attacked by an extradimensional geometrical entity. Villain Cube knows what that's like. He understands what they're going through. He's there for them, to listen as they bare their troubled hearts, and also to set them on fire.
Note: This story crosses over with Equestria Girls, but is set in the pony world.