A little scenario inspired by Carolyn Chrisman's animated short film, "Reversal of the Heart." And I must say that was impressive film she did. ^^
Anyway, here's the plot for the potential episode. Mirage seeks Team Flux's arch enemy, Biff Tannen and pays him to go to the Dragon valleys of Equestria and steal a magic gem stone which legend has it that whoever wears it becomes a dragon themselves. Mirage (in Disguise) sells the gem necklace to Kitty. Kitty puts it on and by her surprise, she is turned into a Dragoness, while maintaining her feline eyes and speech. The rest of the Team momentary panic, confusing her for a real Dragon. But after a closer look, Marty relizes that the Dragoness is Kitty. Doc examines the stone Kitty is wearing and finds out that the gem is from Equestria. So Marty and Dragoness Kitty hop into the Delorean (along with a tight squeeze) and travel to Equestia. They meet Twilight Sparkle who takes our two heroes to Zecora who tells them that the gem is a cursed artefact from the Dragon Valleys and must be returned if Kitty is to return to her original state. As Kitty, Marty and Twilight set on a quest to the Dragon Valley, Biff (with the help of a few lackeys) is sent to make sure they don't make it.
Marty Mcfly, Doc Brown and Biff Tannen Belong to Universal Studios
Kitty Katswell Belong to Butch Hartman and Nickelodeon
Twilight Sparkle and Zecora Belong to Hasbro
Mirage Belongs to Disney
"Reversal of the Heart" Belongs to Carolyn Chrisman