Pinkie has a terrible accident where she is inducted into a horrible nightmare. Madame Mel is a pony she had long forgotten about, and has now appeared in her mind to torment and imprison her. Pinkie must find a way to relieve herself from this darkness, otherwise she will become trapped in her own mind forever.
Not a continuation or remake of Cupcakes, because there are enough of those.
Oooohhh, nice start! Not sure what Pinkie thought she'd achieve by shooting herself out of a cannon, but I suppose that's just Pinkie Pie.