Rainbow Dash notices she's getting a bit of wind resistance during practice drills with the Wonderbolts. So she goes to see Twilight for a quick fix. Twilight finds a spell to help, but only after casting it does she realise it's a prank by a bored mage.

The end result is Rainbow growing a dick, which throws her flight game off even more. To say nothing of the little 'added extras' included within the prank spell's effects. After repeated failures in her drills thanks to her new asset, she's forced to turn to unlikely ponies for assistance...

(This is a request from Superfun)