Happy Halloween! Man, I’m gonna get so much flack for my costuming choices on this one. Oh well. The costumed culprits are, from right to left, respectively:

Letterhead as Wreck-It Ralph
Eddie as The Once-Ler
Pulse as Spike
Serena as Rarity
Cheeko as Pinkie Pie
Lizardbeth as Fluttershy
Fir as Twilight Sparkle
Kit (bite me) as Rainbow Dash
Hinn (a fellow not yet introduced) as Applejack

(rather overtly inspired by this comic)

(also on Deviantart)