If there was an official "Magic of Hatred" in Friendship is Magic.

[Jerry246 44]

Basically my scenario is that in the show's universe Hatred is a cosmic power and ancient and as powerful as Friendship that has been in a constant struggle against it for aeons.  And that many of the villains are in fact agents (slaves) of Hatred that submitted to it's dark will in exchange for power. Here would be ways Hatred incarnate would influence the villains in the series if such a power or entity existed.

Like all negative power in that universe is derived from a central and primary magic of Hatred.

Nightmare Moon and Daybreaker - Corrupted forms that alicorns would take whenever they become corrupted and consumed by the magic of hatred. 

Tantabus - for this scenario, it is an avatar of hatred created by hatred incarnate to punish Luna for "betraying" it

Grogar - a full-time practitioner and fanatically dedicated devotee to Hatred incarnate. Deriving his power from the magic of Hatred with his Bewitching bell being one of the "Elements of Hatred". All the monsters he created have the magic of hatred imbued in them as a result.

King Sombra - A straight-up spawn of Hatred Incarnate itself.  One of many Avatars of Hatred incarnate and is perhaps one of the most powerful as he nearly succeeded in wiping out Friendship singlehandedly in season 9. His crown is also another of the "Elements of Hatred".

Tirek - Fully embraced Hatred Incarnate and willfully submitting to Hatred's dark will in exchange for ultimate power. So consumed by the magic of Hate that it left him with a profound sense of literal emptiness that he tries to fill by absorbing magic from other people and sources. This addiction to the magic of Hate being the cause for his hunger for more power while at the same time serving Hatred's will by absorbing every last magic from sources of and wielders of the magic of Friendship. 

 Queen Chrysalis - The reason why throughout the show she desperately wanted to stay evil and even openly embraces being an "Evil Queen" is because she found comfort for her and her kin in the presence of Hatred incarnate. She is in it's "good graces" and if she reforms or accepts Friendship, there is the fear that it will leave her and she will be left powerless and possibly die or be punished more severely than Luna for betraying it. This is why she embraced being a moustache twirling villain. This is why she rejects friendship and sees it as a disease. This is why she wanted to be evil to the bitter end. Hatred is the only comfort she ever knows.

Storm King - Instead of being a fragment of the Tree of Harmony, it's yet another of the "Elements of Hatred". Like Tirek, he was also seduced by Hatred through promises of power. His storm magic and Strife are manifestations of the power of hatred created by the Staff.

Stygian - Was easily manipulated and corrupted by Hatred incarnate at his most vulnerable and became the Pony of shadows.

Windigoes - Manifestations by Hatred itself that were unleashed upon Ponykind as part of a curse aimed to destroy the wielders and servants of Friendship, it's rival.

Dazzlings/Sirens - one of the many creatures created by or are tools of hatred incarnate as they feed off of the magic of hatred exude by others whenever there is conflict and strife. The reason they reform in the Human world is because they've been severed from the will of hatred incarnate.

King Diomedes and the Thracians -  Hatred incarnate called upon Diomedes and the Thracians to the island they currently live on. One of the several wellsprings of the magic of hatred. Taking advantage of their collective hatred of the other three tribes, it gave them shelter and promises of power in exchange for complete servitude to it's will. And that's how they were able to endure without Friendship. They fully embraced hatred and thrived from it..

For some of these provided examples, the thing that would partially form their hatred and rejection of Friendship would be because Hatred gave them power and game them strength, making Friendship seemingly weaker than it.

Although fictional, the supervillains of the "Power Ponies" could also be agents of Hatred as well. Other entities such as Nightmare Moon's nightmare forces and several "mean 6"clones were created by drawing from the magic of hatred and using that power to create these beings. Basically the mean 6 are also Avatars of hatred like Sombra, albeit somewhat weaker.

In "The end of the End", the great power the legion of Doom gains from the Bewitching Bell is them fully embracing and succumbing to the magic and will of Hatred entirely. every part of them obliterated as they become irreconcilable and irredeemable devotees to Hatred, as it imbues with them great power in a great effort to snuff out and obliterate the magic of it's rival, Friendship,

"Hatred on the other hand, hatred gives you strength! It gives you absolute and ultimate power unlike any other! And what does friendship give you? The answer is clear: Nothing! It gives you absolutely nothing! Friendship is weakness that gives you nothing! Hatred is strength that gives you everything!"

Edited September 1 by Jerry246