Tiberium. The infamous green crystal that destroys entire worlds in its wake of global proliferation. It has been a little over a century since the Tiberium threat was first wiped out on Earth, and with it, the primary vestiges of the Brotherhood of Nod. When the GDI advanced humanity to the stars, they found that Earth had not been the only target of the alien Scrin: dozens of other worlds had already been claimed by Tiberium, and the Scrin returned in full force, attacking human colonies across space, stopping human expansion. To fight back, the GDI undergoes a reformation to become the Interstellar Defense Intiative (ISDI) and enacts the Hallman Directive, designed to stop Tiberium spread wherever it may be; such a protocol brings the reincarnated ITC Methuselah to a planet being ravaged by the green crystal, and the forces under Commander Martin Alexandra deploy to stop the threat.

Crossover Material: Command and Conquer - Tiberian Series/MLP
Rated Teen for Graphic Violence and Language

King Sombra’s dark influence was obliterated by the Crystal Heart, and the villain is well and truly dead. But when he attempts to steal the afterlife of an innocent victim, a human spirit is left hurtling towards Equestria, where this unfortunate soul is revived into the only vessel available: the reconstituted body of King Sombra himself.

Thus, a cheerfully oblivious alien is crammed into the form of the most evil and malicious being Equestria has ever known. Not that Shining Armor and Cadence know this, of course. As far as they are concerned, the King is back and he’s lost his fricking mind.

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TD, the human first seen in No, I am NOT a Brony, GET ME OUTTA EQUESTRIA!!! has been in Equestria for a little over a year now and he's just beginning to fully adjust to his life there. However, when he wakes up one morning to discover that five of the Mane Six have switched cutie marks, he endures a significant change when he helps them out.

He is less than pleased.

Edited wonderfully by Strike89

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Thrust headlong into a strange new world, Solaire of Astora must make amends before he can continue with his mission. Unbeknownst to them all, a shadow from his past approaches.

The Princesses find an alien creature barely clinging to life at the scene of a terrifying crash. Can the Combined Power of the Elements of Harmony save it, or more importantly, should they save it? Will the arrival of this strange creature tear Equestria apart?

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It has been one of the closest guarded secrets of Canterlot's royalty. Deep in a specially constructed dungeon, surrounded by warding spells and powerful magic barriers, exists an enigma. Within a cage that could only be described as something out of a nightmare, it waits and watches all of Equestria. A creature that cannot age, is immune to disease, does not thirst nor hunger, and resists all injury. But, it also holds secrets and knowledge that could safeguard the kingdom. Its powers are frightening, but it is civil enough for debate when patience permits.

Princess Celestia has sought counsel with the creature before, enduring it making deal after deal for its services. The Princess walks a fine line when dealing with it, knowing full well anything could give it an advantage despite its imprisonment. She has had to go back on her word in these dealings, and from this a deep animosity between them has been born. It is a necessary evil as she is convinced this is a being capable of untold evil far and above anything Equestria has ever dreamed of. So long as it remains within the confines of its cell, her kingdom is made safe. So much magic has been woven to ensure that, there is little chance of escape.

So long as the magic holds, there is no danger. So long as the cage remains strong, the nameless creature stays enthralled in his cavernous dwelling. If that were to change--if the magic failed--not even the wisest could say. But one thing is assured, it does not bode well for Equestria.