The excellent background music during and after Twilight's test to determine which is the real Pinkie Pie. Music by William Anderson.
From S3E03 "Too Many Pinkie Pies" of My Little Pony: Friendship is Magic
(And holy crap, has it really been 9 months since I last uploaded BGM? yeesh, sorry)

Like Infinity Dash on Facebook!
http://www.facebook.com/InfinityDashMusic