This is a pretty major one. It looks like that awesome special guest we have been waiting for has finally arrived. Head on down below the break to check out the synopsis!
Thanks to everyone that sent it in!
Synopsis: “Three’s a Crowd”: Pinkie Pie finds her status as “super-duper party pony” in jeopardy when the mysterious Cheese Sandwich comes to town and offers to plan an epic party for Rainbow Dash. Guest voiceover by Weird Al Yankovic.
Update: Song confirmed via Meghan McCarthy's List of episode with songs.
I can't believe this is actually happening.
(Source is Discovery Highlights for January)
UPDATE 2: Episode title was swapped. This episode is probably called "Pinkie's Pride"