Magic

Magic. One word, one syllable, a boatload of meaning. This is easily going to be the most complicated part of the Ponification, and it'll likely take many revisions to get everything balanced - In the end, I might even end up scrapping the entire magic system and building one from the ground up. We'll see what happens!

Overview
Spells - at least Inherent and Residual magic - work in the same way as many of you will remember; some classes get access to a selection of spells, and can then cast these spells a number of times per day for a variety of effects. A main difference is a limitation; only those capable of wielding Essent, such as Unicorns, can use such spells. Aside from that, some other changes as follows:

The Arcane
Ley lines and Essent, Residual, Inherent and Elemental magic, engems and spell matrices, this makes up the bulk of what most would describe as "Magic" within Equestria and beyond.

The Divine
Ley is not the only source of power however, and those with the strength of character and sheer unflinching devotion to the deific forces in the world can themselves wield power rivalling any mage.

Mechanically speaking, Divine magic does not require much modification to fit into the setting; a devout acolyte of Celestia could feasibly channel a portion of her power and create miracles from it, such is the basis of all divine magic.

Alternatively, the devout could have sworn themselves to one of the Elements of Harmony - in this way operating as a Domain Cleric - or to all of them combined, which could be the equivalent of Celestia.