Twili's missing party guest

Part 1: [link]
Part 2: [link]
Part 3: [link]
Part 4: [link]
Part 5: [link]
Part 6: [link]
Bonus comic! - [link]
Part 7: [link]
Part 8: (Here)
Extra! - [link]
Part 9: [link]
Part 10 (END): [link]

I had the perfect thing for Twilight's explanation and then forgot it... Darn. Still makes sense I hope.

EDIT: Twilight's cutie mark added in! Cheers to ~KrazyKatt11 for pointing that out.