This is my interpretation of witches in the G4 universe of the MLP franchise. The idea came from the witches from the G1 movie and what I would do to expand on their lore.

Witches (or Warlocks when referring to males) are a type of Human who are born with the power to control magic and use spells, witches reside in a realm sperate to the human world known to outsiders as the Witch(ing) World. Most Witches see it as their priority to Spread Fear and hatred in the human world, as well as other realms they gain access to. Witches accomplish this through conjuring their spells, tricking people into ingesting magic potions, or through other practical means whether magical or not (i.e. kidnapping, murder, theft, and others.) They are entirely human, yet possess magic that is different under a different code from unicorns (as well as other creatures from Equestria), fae, and sentient magical beings. Witches are considered as monsters or demons due to their relationships and interactions with non-witches, but they are not inherently evil, the ancient witches had no choice but to adopt this lifestyle when they separated themselves from the rest of humanity and elected a Warlock, who is only known as 'The Witch Master' to lead and defend them from threats to their kind.

This is what I have so far for my witches. If you have any questions don't be afraid to ask, it will help me build them more.