How do you think Lightning Dust got her cutie mark?

5353606 Well, considering she's Rainbow's foil maybe she preformed a trick of her own that's just gone unnamed.

5353606 Probably in a similar fashion to Rainbow Dash's, likely with a special signature trick of her own.

I think this scene is the reason: http://ask-downer-dust.tumblr.com/page/4

Keep scrowling down...until you'll later find out the REAL reason why.(This Tumblr has been cancelled...which is sad because it was a good tumblr in my eyes)