Tirek

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A lot of people say this guy is the Lucifer of My Little Pony and, to tell you the truth, I gotta agree on that. For the very first villain of the franchise (it's 1984, remember that), he's one sinister son of a bitch.

But who is he anyways? Let's start with him surrounded by utter darkness, giving commands to his servant Scorpan (in his mind "the most pathetic servent I've ever had") and punishing Spike for his ineptitude (in his mind, Tirek's like "I'm in a good mood to decapitate this baby dragon"). His foot soldiers may look intimidating, but its his army of dragons the real threat.

Strength is all that matters and he confirms such thing when he eventually transforms some ponies into dragons, just to use them for a medium to unleash the rainbow of darkness to bring the eternal night (Well whaddya know? Nightmare Moon wasn't the only one that thought the same plan). The screams of agony of the ponies satisfy the centaur, but as for Scorpan, it pisses him off.

Then, a war starts between the forces of the rebellious Firefly and the army of Tirek. After giving a beatdown to Scorpan for his alignment to Firefly's forces, the centaur attempts to achieve his plan high in the skies thanks to a group of dragons. However, Firefly goes higher than him and, by using the weapon of mass destruction, the rainbow of light, only a massive explosion is seen. That's right: Firefly literally nuked Tirek.

The End… oh, and yes, Spike survived.