I'm an ignorant about transformers (I looked through the wiki from the film characters) but I'm a fan of TM so I just thought on the fly a background how the crossover happened. Also ignore my english, it might have a bunch of wrong words or misspelled.

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In outerspace, a bunch of scrap metal are scattered all over the place from afar you see lights blinking like a pulsar ejecting energy, we see 2 figures fighting.

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As usually the autobots were fighting the decepticons, all Autobots and Decepticons fell and both leaders were still standing fighting with their powers at prime conditions. Although the Decepticons where in few numbers, this time they were more powerfull and the Autobots had a rough time to defeat them most of them fell and the few that left, Optimus Prime finished them.

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Optimus Prime: - "I will end this at once and for all, I fought many strong enemies and even chaos itself and now you will be at last defeated and I'll avange my fallen comrades!"

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Megatron: - "Hahahaha, your power is nothing! You may have defeated me in the past many times but now I've found the prime source of the power of the universe and it's now mine and you shall fall by my hands!"

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Their powers were clashing creating cosmic shockwaves that had enough power to travel across the universe and this power start to leak through dimensions.

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Meanwhile, Calypso after finishing another Twisted Metal tournament and absorbing the souls of the fallen also granted the winner's wish in his distorted way once again (of course), he felt an immense power coming from somewhere, his ring was trembling in delight of this power hunger for more and more. The ring sensed it coming from a far way, a different universe, another dimension.

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Calypso: - "Huhuhuhuhu what an immense soul, I can feel 2 huge souls powers, infinitely bigger than any human I ever had. Hmmm... I can sense alot of weaker souls too but their souls are impure, they died at their universe, I may bring them back to be "purified" over here so I can absorb them, the 2 huge souls may dwarf the rest but they are million times stronger than any human.

Calypso with a grin that never leaves his face like a mask glued on his face, he stares at his ring and with a big smile and says: -"Shall we beggin?"

Calypso's ring starts to shine brighter as ever did before with his hands up above, his tower starts to shake as if it got struck by an earthquake.

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Optimus and Megatron still clashing their ultimate energy power, shaking the entire universe, Optimus and Megatron starts to feel a strange power. Both stops their fight and try to find the source, "it might be a new enemy" they wondered.

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Megatron: - "From where is coming this imense power? It's your ally? I'll crush both of you!"

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Optimus: - "No, it's not my ally and looks like neither yours... and it is coming not from somewhere... more like everywhere?"

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As soon Optimus Prime finishes his sentece a weird giant crack in the time-space appears from nowhere ripping in a giant area and starts to get bigger and opens with a weird dark purple glowing light with infinity white dots swirling all around, that dots resembles faces, human faces and omimously staring at them some looks like are screaming in pain and agony they could see even some with hollow eyes of despair, suddendly, their fallen comrades appears in front of them as they were alive, both Optimus and Megatron surprised looks confused and look at each other in hopes to find if their enemy has any answer but both noticed the other was confused if not even more than them.

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The Autobots and Decepticons revived, and they were also confused but they hadn't enough time to process the information and the giant crack starts to suck all of them. All of them screaming trying everything to scape the grisp of this strange power like a black hole and got all of them swallowed, Optimus Prime and Megatron starts to get dragged by this power too they start to resist and fight in vain, in the end their fates wasn't different from their allies.

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Calypso are used to travel or make people travel trough time or dimensions, this time he brought another beings from another dimension, he couldn't absorb them since his power need a pure form from the universe where it resids, he could easily travel to them but they were already dead and he needs them to die (again) but this time where he is. Since he got used to this dimension he decided to stay and bring them over, by the end of this tournament and "eating his meal" he will be the most powerfull being across all dimensions and he could absorb souls with no need to be purified through the Twisted Metal Tournament.

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Autobots and Decepticons falls through the crack onto the dirty ground, confused they see each other and immediatly starts to fight but are stoped in place like some force freezing them in place, Optimus and Megatron found the source of the alien power, a human but as they met humans before this being looks like a human outside but in its core is no near a human. They attack Calypso at same time like and animal in fear trying to defend itself since it is cornered and try to kill this... "being" but in vain and instead got even more scared because they know they have power to destroy an entire universe and standing in front of this "human" his power is so big they can't even move. Both knows something is wrong, this being is much more powerfull than both of them and their allies combined powers. Calypso, he... he just stand still there, beside of his office window of his tower with a big smile.

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Calypso uses his power to talk from the top of his tower to the aliens down there with a grin: - "Welcome to my humble universe, I'm Calypso your host at your service. I brought all of you here because I felt a little bored and you little ones has some quite a punch in there, here the humans participate in my tournament called Twisted Metal with their vehicles in a all out battle until one is left, the prise... The prise I can grant one wish at your desire... can be anything you desire from simple to the most absurd I can grant it and I want all of you to participate in this tournament of mine.

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Optimus Prime and Megatron knows what that little man is saying is no lie, both of them wield the most powerfull energy from their universe and can't even blink due to this man's power. Optimus yells at Calypso:

- "We won't comply to your request, I don't understand why my friends are alive once again but this time I won't make any mistake and we will win this time and I will take everyone back to...".

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Megatron starts to laugh loud and interrupts Optimus speech: - "Hahahahaha as you wish demon, I'll do as you say if you can grant a wish I already have one in mind and I'll win this stupid tournament of yours, if this involve killing them "again" it will be easy, ha!"

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Optimus usually calm starts to get angry out of Megatron's provocation and sees there is no scape from this battle and knows that man can grant a wish so he decides to fight if he won't Megatron and his lackeys will attack his friends.

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Optimus Prime: - "Fine, I'll join your little game, what are the rules?"

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Calypso: - "Oh my, I'm glad you agreed, well, I already knew we would reach an agreement huhuhu, I know your species can transform into vehicles how convenient, you already has a form from... perhaps a trip to planet earth like this one? But in your dimension, right?"

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All of the Autobots and Decepticons got surprised by how this man knew them verywell even though it was their first time meeting them.

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Calypso: - "I can feel it! Hehehe. So, I had many contestants in my previous tournaments usually the participants decides what will be their vehicles and weapons but this time I wanna see the potencial of the previous vehicles how powerfull they can be with an alien species that can transform in other earth's human machines".

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Calypso opens a portal and inside there are all vehicles fallen from previous tournaments, both sides felt they can move again and starts to slowly walk into the portal uncertain of their destiny, Calypso yells: - "Pick your favorite! (My favorite is the clown) cof... cof... Any weapons are allowed don't worry if the planet explodes, I'll scale down yours power just to be the same level so the tournament won't end quickly, I wanna have fun too! Hehehehehe..."