whoa whoa, wait, game design? Ho shit, now we're talking my language...
Given that the ponies major meathod of attacking is bucking, which requires them to face
away from the target, active combat is next to impossible, so a final fantasy style TBC system is the most reasonable choice, with the bucking animation being your basic 'attack' command. Different breeds would have racial abilities, most likely, maybe even falling into different class roles - earth ponies would likely be tank and heavy hitters, Pegasi would be your rogues, capable of doing things like distracting the enemy and using quick attacks, and unicorns, of course, would be your mage-type classes.
of course, that said it does make me think that an active battle system might not be impossible - there may be pony-designed weapons, for example, which would allow for direct attacking, and having the controlled character be a unicorn would make that even easier, without the need to design the weapon around a lack of thumbs. A pegasi PC would be the most diffictult to deal with, because of the flight - it could be done in a meathod similar to the flight in Brutal legends, wherin the player can only attack while on the ground, bu then we're essentially an earth pony with a bit more mobility - not a terrible thing, but difficult to reason with thematically, and reconciling the combat with flight could be pretty tricky, but if pulled off well it could be pretty rewarding...all this is only theory, of course, Considering the characters would need to handle differently from almost any other game it would require lots and lots of playtesting to come up with anything solid - making it difficult to greenlight, because it would mean several months of work to even see if it's viable.