I just thought I would indulge both the brony and hard core Star Wars fan in me for a second and just add my thoughts on which lightsaber combat forms would best fit the Mane 6. For those of you that don't know there are 7 forms of lightsaber combat in the Star Wars universe and though they are not mentioned by name in the movies they are in multiple expanded universe works and are considered canon.

http://starwars.wikia.com/wiki/Lightsaber_combat

Pinkie Pie: Form I known as Shii Cho best fits her because it is known for being extremely random and unpredictable with its broad sweeping motions and unconventional tactic of completely letting lose of control. All jedi padawans learn this form first but few have truly mastered it and one of those few is Kit Fisto who was the jedi that aside from Mace Windu lasted the longest against Darth Sidious when the jedi council tried to arrest him.

Rarity: Form II known as Makashi best suits Rarity as it is the most elegant of all lightsaber forms. Based heavily on classical fencing it focuses on fancy footwork and efficiency of movement, it was invented to counter lightsaber wielding opponents but is weak against blaster wielding opponents and more strength based lightsaber combat forms but can be compensated with through extensive training. The most well known practitioner of this lightsaber combat form is Count Dooku.

Fluttershy: From III known as Soresu best suits Fluttershy as it was invented by jedi who preferred to take a more passive/defensive approach to lightsaber combat for fear of more aggressive forms leading them to the dark side. Its defense is solid but its offense is sorely lacking and because of this is often combined with other lightsaber forms to compensate for this. Obi Wan Kenobi who is the most well known practitioner of this studied Soresu with the intend of making a hybrid form of it and Form IV ataru which his master Qui Gonn Gin specialized in.

Rainbow Dash: Form IV known as Ataru best suits Rainbow Dash because it is the most heavily focused of all lightsaber combat forms on speed and force assisted acrobatics. It and Form V were invented by jedi Soresu masters who wanted to address the lack of offense in Soresu. The best known practitioners of Ataru are Qui Gon Gin and Master Yoda, Master Yoda used this form to compensate for his small stature and turn what is ordinarily a weakness into a strength.

Applejack: Form V known as Shien/Djem so best fits Applejack because it is one of the most physically demanding of all lightsaber combat forms. It builds on the strong defense of Soresu and also provides and equally devestating offense. Shien was made to counter blaster wielding opponents while Djem so was made to counter lightsaber wielding opponents. Lighstsaber duelists who are tall and have large reserves of brute strength such as Darth Vader, Luke Skywalker and Darth Bane often favor this form.

Twilight Sparkle: For VI known as Niman best fits Twilight Sparkle as it is most often used by consular jedi who often focus more of the intellectual side of the jedi order as opposed to jedi guardians who see alot of combat. It was invented by jedi consulars who saw Ataru and Shien/Djem so as too aggressive and close to the dark side. It combines moves from all previous lightsaber forms into a basic easy to learn style that also make its easy to chain force based attacks into lighstaber combat sequences. Though some such as the fallen jedi turned sith named Exar Kun took this lightsaber combat form above and beyond what was intended and became true jacks of all trades.

I know the last one is a variation of Fluttershy but I had an extra spot and had to fill it

Flutterbitch: Form VII known as Juyo/Vaapad best suits Flutterbitch because it is the most aggressive and deadly both of lightsaber combat forms both to its victim and user. Juyo can best be described as the lightsaber combat version of a berserker rage mode, its uses ones inner darkside to greatly amplify strength, speed, endurance and force aptitude. It is like Ataru and Djem So had a very evil vicious child from the darkest bowels of hell except with it lacking the strong defense of Djem So. Juyo was later refined by Jedi master Mace Windu to address the lack of defense and to try to allow the user to still tap into their inner dark side while not succumbing to it, he trained two of his padawans Sora Bulq and Depa Billaba in Vapaad but they succumbed to their inner dark side.