This is basically an alternate universe type of story, a crossover with the lego movie.

Big Macintosh is a boring, blank slate, he followed the rules down to a T, and follows what others do. When he sees a perple unicorn mare rummaging around a pile of building supplies and apples he had demolished, and fell down a giant hole, he ends up finding a piece da resistance and meets the mare from before, who is trying to defeat President Sombra.

Big Mac: Emmet
Twilight: Wild Style
Fluttershy: Blind wizard Vitruvius
Sombra: President Business/lord Business
Rainbow dash/ Applejack: Bad Cop/good Cop
Trixie: Batman
Bulk Biceps: Metal Beard
Pinkie Pie: Unikitty
Scootaloo: Benny

I need a better one for Benny.

But what of metal beard? maybe Pip?

3328360
I put bulk biceps for metal beard.

3561085 Well maybe make Derpy as Benny, either her or Lyra