Similar to how once upon a time Twilight had to make friends to deal with villains from Princess Celestia's past, Luster Dawn finds herself teamed up with a belligerent foul-mouthed changeling to deal with a villain out to avenge a villain from Twilight Sparkle's past :D

Yes, Luster Dawn calls him fuckhead as he leaves and, without magic, manages to stop his little alchemy experiment there thanks to something Trixie taught her: she can mix the sulfur, saltpeter, and charcoal he left lying around to make gunpowder and blow it up. The benefits of having a mother who makes pyrotechnics for her act :D