Tirek

Tirek is the main antagonist of the Season Four finale episodes Twilight's Kingdom Parts 1 and 2. He is an escapee from Tartarus a dark land that serves as a prison for many horrific entities, and possesses the power to drain ponies of their magic. This Tirek is significantly different from his older counterpart - he has no army nor access to the Rainbow of Darkness, and instead relies on his own magical powers - but he shares the old Tirek's status as the most powerful and evil villain of his generation so far.

In Rescue at Midnight Castle
He resides in the forbidden Midnight Castle alongside his minions and his servant/slave Scorpan, who he orders to kidnap the ponies of Dream Valley to execute his evil scheme.

Tirek wields the Rainbow of Darkness, a powerful satchel containing evil magic which corrupts everything it touches. It can even turn the ponies he captured into evil dragons which were used to pull his "Chariot of Darkness" and execute the event called the "Night that Never Ends", on which he will use the Rainbow of Darkness to corrupt Dream Valley and plunge it into chaos. When Tirek takes off in his Chariot of Darkness, Megan grabs the satchel containing the rainbow of darkness, but can't hold on to it. As he was about to release the Rainbow of Darkness, Megan opens the locket to reveal the Rainbow of Light. But it's only a small piece that is soon enveloped in darkness. But the Rainbow of Light starts fighting back, and eventually overpowers the Rainbow of Darkness. Tirek was destroyed by the Rainbow of Light, freeing Scorpan from his spell and turning him back into his human form.

In Twilight's Kingdom
Tirek and his brother Scorpan tried to take over Equestria; but when Scorpan became friends with Starswirl the Bearded, he came to appreciate Equestria and tried to turn Tirek away from his quest. Tirek refused, so Scorpan warned Princess Celestia and Princess Luna, who were able to imprison Tirek in Tartarus.

When Cerberus left his post at the gates of Tartarus (in episode "It's About Time; for unknown reasons) Tirek was able to escape. Sometime after he began absorbing a unicorn's magic. Celestia received a vision of this and sent Discord after Tirek. However, Tirek was able to manipulate Discord into betraying his friendship with Fluttershy and joining his side. Tirek began eating energy from pegasi and earth ponies to take away their flight and strength. Finally he went after Celestia, Luna, and Cadance, but finding their magic to be gone he imprisoned them in Tartarus. Discord thought Tirek didn't value him as a partner so Tirek gave him his medallion, saying that it was his only keepsake from someone close to him. Then Tirek saw a stained glass window of Princess Twilight Sparkle, and Discord explained to him who this new princess was. He and Discord captured Rainbow Dash, Fluttershy, Applejack, Pinkie Pie, Rarity, and Spike, and Tirek ate their power before doing the same to Discord, saying that his medallion actually came from Scorpan, and that Discord is as worthless to Tirek as Scorpan was.

Growing to tremendous size from the magic he absorbed, Tirek attacked Twilight, and when he destroyed her library, she became enraged and fought him in an epic battle. The two were evenly matched, though Twilight seemed to have a slight advantage, so Tirek revealed the other Mane 5, Spike, and Discord, imprisoned in orbs. Tirek told Twilight to give him her magic and that of the three Princesses, and she agreed, so Tirek released all except Discord. Twilight told Tirek to release him as well. He accepted and then ate Twilight's magic, increasing his size to massive proportions. To thank her for her kindness, Discord gave Twilight Scorpan's medallion which was the final key to the Tree of Harmony box. Unlocking it, the Mane 6 received Rainbow Power, which they used to blast Tirek with a rainbow not unlike the one produced by the Elements of Harmony, leaving him imprisoned in a cage in Tartarus with no power while restoring Equestria and the ponies to the way they were.

Rivalry with the Diesel Squad
In Pooh and Brian Griffin's Adventures of Transformers: Age of Extinction, Tirek made a deal with them that if they help him and the villains and provide weapons, then he'd give them their own kingdom to rule. But the Diesel Squad only agree when Tirek promises not to harm, banish, or kill Princess Celestia. But then in Brian Griffin vs. The Mummy: Tomb of the Dragon Emperor, they witness Tirek about to blast Thomas, the Sparkles, and the Princesses, but are saved by Percy. At this point the Diesel Squad realize that Tirek double crossed them. Later on, they turn against the villains and kill Queen Chrysalis. Then they ask for a truce and join the heroes' side and help them defeat Tirek. During the battle, Megatron intervenes, incapacitating Tirek. Weaken by the powerful Decepticon Fusion Shotgun and our heroes' modern weaponry, Tirek loses all his power [even when a bullet manages to cut through his shoulders]. Then the Diesel Squad face Tirek themselves, but then Tirek protests that they had a deal and even brings up how he gave them his medallion to show that his loyalty to them. But the Diesel Squad then say how he promised not to kill the Princess Celestia, but after witnessing him about to blast not only Princess Celestia, but her sister, niece, nephew-in-law, and her students, it showed that he double-crossed them, thus breaking the deal. Then Scor-Brein crushes and breaks the medallion with his claws. Then the Diesel Squad decide to show Tirek what happens when someone double crosses them and they start to battle Tirek in manly fashion. And due to their strength and training they weaken Tirek even more, and then using his abrudent strength and claws, Scor-Brein tears Tirek's horns clean off his head, thus making him unable to conjure magic anymore. Dusty then reveals the "Rainbow of Light" which consumes Tirek and results to his death. Afterwards, Princess Celestia grants them the prevlige to be honored guests to Canterlot, but warns them that they will be consequences if they go back to their old ways.

Relation with Megatrain
Years ago, Megatrain had resurrected Tirek so he could steal energy but Tirek betrayed him and stole Megatrain's arc [which gave Tirek his ability to steal magic] then he put Megatrain in the prison of the Deceptitrains. Then when Tirek returned to Equestria, he discovered that Megatrain's machine was in one of the mountains of Equestria, but he was sent to Tartarus. Then when he returned again, he gained enough energy to be a god. But the Mane 6 defeated him and sent him back to Tartarus. Years later, Tirek returned seeking revenge and intending to start the machine up and use Megatrain's army of Deceptitrains for his own purpose, but found out that he needed the Matrix of Leadership in order to start it up. Optimus gave the Matrix to Thomas who had become a Prime himself, to prevent Tirek from succeeding along with the Blue Ruby and the Black Pearl. When Tirek had arrived in Canterlot looking for the Matrix he was denied to find out that it is only in posession of a Prime not the Princesses. When he come to Optimus and found out that he didn't have the Matrix, he froze him into an ice statue. Then found out Thomas had the Matrix, the Princesses raced to Thomas and warned him. But Tirek had followed and demanded Thomas to give him the Matrix. Blue Ruby, and Black Pearl. And if he did, he'd let him live to be his own train. But being loyal to Optimus, Thomas denied. In which Tirek blasted him, seemingly vaporizing him. But he inatvertinally activated a spell that brought Megatrain back. Megatrain was pleased to be free but then he took his fusion, plasma cannoin and vaporized Tirek completely for betraying him. When Tirek was killed pernamentally, Megatrain took back his Arc and got his energy back.

Powers
Tirek wields the Rainbow of Darkness, a powerful satchel containing evil magic which corrupts everything it touches. It can even turn the ponies he captured into evil dragons which were used to pull his "Chariot of Darkness" and execute the event called the "Night that Never Ends", on which he will use the Rainbow of Darkness to corrupt Dream Valley and plunge it into chaos.

In his first appearance, Tirek is shown to be able to consume the magic of ponies, removing their cutie mark in the process - he seems to literally suck this magic into his mouth, like a more kid-friendly version of "soul stealing". A pony drained this way is completely stripped of all magic. Tirek adds the stolen magic to his own, increasing his size and power. The more magic he drains, the more powerful he becomes. After devouring enough unicorn magic, he becomes able to strip pegasi and earth ponies of their innate magic as well. At very high levels of power, he becomes able to strip even an alicorn or a draconequus of all magic. If Tirek drains the magic of every single pony in Equestria, he effectively becomes its God, able to single-handedly control all the aspects of the land that ponies normally regulate collectively.

But in Pooh and Brian Griffin's Adventures of Transformers: Age of Extinction, Tirek receives a stronger power when he eats energy crystals that come from The Miner Trains' mine. So in the movie the villains aquire 17 trucks full of crystals to help Tirek grow stronger. However, after eating the crystals, he can no longer steal magic form equines, being who posses it, and objects that contain it. Much to his disappointment. But then our heroes take the train carrying the crystals near the end with the villains in pursuit. After a wild chase, the villains manage to get the crystals back but our heroes catch up and take back 14 of the trucks while the villains plumment off a bridge the Miner Trains blew up and are buried by the crystals in the water bed. But some of them manage to escape.

Then in Brian Griffin vs. The Mummy: Tomb of the Dragon Emperor, when the Emperor gets his powers back, Tirek finds some more crystals and grows bigger. But later on, when the Diesel Squad turn against the villains, Dash-9 shoots Tirek his power drains and he shinks. Which means that when when he is shot at by guns, explosives, and other modern weaponary he loses his power he has built up on and shinks back to his weakest form. Then after the other villains are defeated, Tirek is about to kill Princess Celestia, Luna, Cadance, Shining Armor, and Thomas when Megatron intervenes, by firing at him with his fusion shotgun. Which the power shotgun is too much for Tirek who has never been hit with a powerful blast, then our heroes fire all their guns and weapons at Tirek which overpowers him, then 2 stray bullets cut through his shoulders and he loses all his power and he returns to his weakest form. Then he is killed by our heroes.

Then in Thomas' Place as a Prime, he eats some energy crystals and his powers and strength grows back to strong mode. But he is seeking the Matrix, Blue Ruby, and Black Pearl, intending to use them to increase his powers and bring back Megatrain's army for himself. Then he found out Thomas was now a Prime thanks to a flag and releized he had the Matrix, the Princesses raced to Thomas and warned him. But Tirek had followed, Thomas battled Tirek and due to him holding the magic gems he could fire beams of magic from his gatling guns. The 2 reached a stale mate so Tirek demanded Thomas to give him the Matrix. Blue Ruby, and Black Pearl. And if he did, he'd let him live to be his own train. But being loyal to Optimus, Thomas denied and stated how he would keep to the Prime's code. In which Tirek blasted him, seemingly vaporizing him as our heroes watched in shock. But by hitting Thomas, he inatvertinally activated a spell that brought Megatrain back. Megatrain then walked up to Tirek and pointed his cannon at Tirek planning to kill him in whoch our heroes were confused. Megatrain then explained about how he resurrected Tirek so he could steal energy but Tirek betrayed him and stole Megatrain's arc [which gave Tirek his ability to steal magic] then he put Megatrain in the prison of the Deceptitrains. And when Tirek blasted Thomas, he inatvertinally activated a spell that brought Megatrain back, then he took his fusion, plasma cannon and vaporized Tirek completely for betraying him in which Optimus was restored to his own true form. When Tirek was killed pernamentally, Megatrain took back his Arc and got his energy back. Afterwards Tirek had to rely on the Rainbow of Darkness once again.

In Thomas' Adventures in Transformers Prime
In Thomas' Adventures in Transformers: Prime, Tirek's anti-spirit talks to Bowser in another dimension. Bowser was confused for a moment, then Tirek explains how he was cremated and that his anti-spirit has survived. And he now control's Bowsers body to travel to Cybertron, and he explains he want's to make his own Decepticons, and explains that he need another constitution for revenge against the Diesel Squad. When he is confronted by Thomas, Bowser deceives him, but Tirek groans him in pain. But when Unicron gets the Matrix he and Tirek get sucked in. When Megatron disbands the Decepticons, Bowser is still on Tirek's plan but is killed on the train chase.

In Return of the Big Bad
In Return of the Big Bad, Tirek's anti-spirt escapes and boy is he angered to the top. His spirit then gather up the remaining Deceptitrains and order them to make him a new body, something even more scary then his other one. And stronger too. Soon enough they gather up enough

Tirek's comet
Before Tirek betrayed Megatrian he made a comet that will strike Equestria for every 1000 years. in Age of the apocalypse, Princess Celestia explained about the comet and it would strike friday afternoon, ending all the equines in Ponyville, Cloudsdale, Manehatten, and everywhere in Equestria! Once they destroyed the villains army the comet was in the atmosphere, and Princess Celestia explains that the only way to stop the comet she must push it away into a black hole. Which she does. Then as she pushes the comet into the black hole, she starts to lose her strength and is close to death. But the Dragon bots save her, before she loses her strength.

Attempts to harm, banish, or kill the Princesses
In this film, Ernie and the Dazzlings travel to Tartarus, to find Scorpan. They find Tirek and made a deal with him. Then after he absorb all magic, Diesel 10 joins the party. When Ernie shows the Princesses Brian's collar believing he's dead, Tirek sends them to Tartarus. Then Gollum attacks and the villains show up, but our heroes battled Tirek, while Peter fighst Ernie. But soon after Gollum was killed, the ring destroyed and Sauron obliterated. Brian uses the gems to absorb all of Tirek's powers and the Princesses are free. Tirek hires the Diesel Squad to provide weapons for the villain army, and that if they help him and the villains then he'd give them their own kingdom to rule. But the Diesel Squad only agree when Tirek promises not to harm, banish, or kill Princess Celestia. In this film, Tirek is about to blast Thomas, the Sparkles, and the Princesses, but are saved by Percy. At this point the Diesel Squad realize that Tirek double crossed them. Later on, they turn against the villains and kill Queen Chrysalis. Then they ask for a truce and join the heroes' side and help them defeat Tirek. During the battle, Megatron intervenes, incapacitating Tirek. Weaken by the powerful Decepticon Fusion Shotgun and our heroes' modern weaponry, Tirek loses all his power [even when a bullet manages to cut through his shoulders]. Then the Diesel Squad face Tirek themselves, but then Tirek protests that they had a deal and even brings up how he gave them his medallion to show that his loyalty to them. But the Diesel Squad then say how he promised not to kill the Princess Celestia, but after witnessing him about to blast not only Princess Celestia, but her sister, niece, nephew-in-law, and her students, it showed that he double-crossed them, thus breaking the deal. Then Scor-Brein crushes and breaks the medallion with his claws. Then the Diesel Squad decide to show Tirek what happens when someone double crosses them and they start to battle Tirek in manly fashion. And due to their strength and training they weaken Tirek even more, and then using his abrudent strength and claws, Scor-Brein tears Tirek's horns clean off his head, thus making him unable to conjure magic anymore. Dusty then reveals the "Rainbow of Light" which consumes Tirek and results to his death. Afterwards, Princess Celestia grants them the prevlige to be honored guests to Canterlot, but warns them that they will be consequences if they go back to their old ways.
 * Brian Griffin's Adventures of The Lord of the Rings: The Return of the King
 * Pooh and Brian Griffin's Adventures of Transformers: Age of Extinction
 * Brian Griffin vs. The Mummy: Tomb of the Dragon Emperor

Trivia

 * Tirek was originally a G1 villain who was the main antagonist of Rescue at Midnight Castle.
 * While Tirek was likely meant to outshine previous villains such as Chrysalis and Sombra, many fans hate him for destroying Twilight's library and sending the princesses to Tartarus. Some have even speculated, out of hate for Tirek, that after his reimprisonment, Cerberus eats him as punishment for sending the princesses to Tartarus. This is the exact opposite scenario of Chrysalis and Sombra; When they died, most fans denied it out of love for them or desire to see them return (and the IDW comics, whose writers are bronies and pegasisters, had Chrysalis survive, while some continue to deny Sombra's demise even after it was confirmed). This, in turn, could likely be the reason why Meghan did not have Tirek end up like his G1 counterpart.
 * Tirek will become Thomas' enermy in Thomas' Adventures of My Little Pony Friendship is Magic - Twilight's Kingdom (Full Movie)
 * Tirek will get his revenge on Thomas and Twilight in Thomas, Twilight Sparkle and the Adventures of Rocky and Bullwinkle, Thomas and Twilight Sparkle Visits The Haunted Mansion, Thomas and Twilight Sparkle's World of Color, Thomas and Twilight Sparkle's Adventures of Disneyland Fun, Thomas and Twilight Sparkle's Adventures of Disney's Villains' Revenge and Thomas and Twilight Sparkle in Fantasmic (Walt Disney World Version).
 * Tirek will guest star in Brian Griffin's Adventures of The Lord of the Rings: The Return of the King and sends the Princesses, to Tartarus, Pooh and Brian Griffin's Adventures of Transformers: Age of Extinction and Brian Griffin vs. The Mummy: Tomb of the Dragon Emperor.
 * Tirek is also The Diesel Squad's arch rival.
 * It is revealed in Brian Griffin's Adventures of Transformers: Age of Extinction, energy crystals give an even better power than magic does and in Brian Griffin vs. The Mummy: Tomb of the Dragon Emperor' when he is shot at by guns, explosives, and other modern weaponary he loses his power he has aqulataed on and shinks back to his weakest form.
 * Tirek is killed in Brian Griffin vs. The Mummy: Tomb of the Dragon Emperor but returns in Brian Griffin's Adventures Chronicles.
 * Tirek is friends with Hunter before he went to Tartarus and was killed by our heroes and then betrayed Megatrain. But then in Revenge of the Deceptitrains, Hunter resurrects him and goves him a second chance. But after Hunter is killed, Tirek is then Killed by by Samurai OpThomas Prime and then his body is cremated by Duncan's flamethrower, thus killing forever and ever. But in Thomas' Adventures in Transformers: Prime, his anti-spirit has surveyed and controls Bowser body. But he and Unicron are sucked in the Matrix
 * Tirek will become Jimmy Neutron's enemy in Jimmy Neutron's Adventures of My Little Pony: Friendship is Magic - Twilight's Kingdom.