Apple Bloom meets somepony who's just as much into potions as she is, and soon becomes enamored with her to the point of not allowing anything but perfection in her work. She ends up learning a lesson she'll never forget.
Twilight Sparkle and Potion Nova work to make the Cosmos Elixir, but after an embarrassing moment makes Twilight run away, she discovers that Potion Nova may have quit making potions altogether.
After their wedding, Rainbow Dash, Starlight Glimmer, and Spike are now husband and wives. This is how they gave birth to their new child, and how she came to be.