In the first Halloween themed episode, Applejack is dressed as a scarecrow, in this one she's a lion. Scarecrow and Lion are both characters from the popular book/movie The Wizard of Oz (1939).
Fan favorite Derpy can be spotted in the maze dressed as Twilight.
During Fluttershy's spooky tea party, her "unannounced guests" are Utena from "Revolutionary Girl Utena", Ranma from "Ranma 1/2", Rei from "Evangelion", Bulma from "Dragon Ball Z", and Sailor Moon from the show of the same name, "Sailor Moon". All are referring to popular anime. Spike's voice actress Cathy Weseluck was the English voice of Shampoo of "Ranma 1/2" and also did the English voices of Chiaotzu, Puar, and Kid Trunks for the Vancouver English dub of "Dragon Ball Z". While Rarity and Granny Smith's voice actress Tabitha St. Germain did the English voice of two characters in "Ranma 1/2" and was the English voice of Gotenks for the Vancouver dub of "Dragon Ball Z". And finally Fluttershy and Pinkie Pie's voice actress Andrea Libman did the English voice of young Chi-Chi for the 1995 English dub of "Dragon Ball" and Penny from the first English dub of "Dragon Ball: Curse of the Blood Rubies".
Got leaked online early, a whole month before its intended release.