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Also, I should note that the comic writers make plenty of homages and nods to G1.
When they were writing the comic arc for Nightmare Rarity, I'm sure they looked to Tirek when they were writing what happened with Nightmare Moon.
Except, instead of Tirek controlling the Rainbow of Darkness, the Nightmare Force was controlling Luna.
The Rainbow of Darkness and the Nightmare Force were the exact same thing. Both acted sentient, both could corrupt the hearts, minds, and form of living creatures.
The only thing the Nightmare Force could not do that the Rainbow of Darkness did was corrupt the land itself, too. Nightmare Force really REALLY wanted Luna's kingdom. The kingdom of eternal night.
Tirek exists in G4 too, but is probably long since dead. Like his G1 counterpart, Tirek has no power of his own. Did he inspire Luna to go mad with power? Well…