Let's face it, Violenjaegar is practically a no-brainer for the Movie universe. His original background goes like this: "Violenjaegar is a mysterious, evil entity who revived and restored some of the greatest Destron soldiers to serve as his generals. But on their defeat, he revealed his true nature - he is a horrendous creature composed of the wrath-filled souls of vanquished Destrons." Now, why is he a no-brainer? - He's obscure. Only a small portion of the fanbase really knows who he is, so more liberties can be taken than with Prime, Megatron or Starscream. He's effectively a blank canvas that the writers can work with. - He's able to summon up deceased Transformers to serve him. In other words, he can call up all the guys who died in the first two films, allowing the CGI models to be recycled. He's economical! - Story-wise, he fits right in with Revenge of the Fallen. The death of The Fallen, last of the Ancient Primes, awakens / summons / empowers Violenjaegar. Heck, the exposition for him is easy: "Our ancient sages speak of this being. He once rose on Cybertron, following a great battle between our two factions. Like a parasite, feeding off the last remnants of the dying, he grew in power, until both our sides had no choice but to put aside our differences and seal him. But the seal must have been imperfect. When I killed The Fallen three years ago, I must have released enough energy to free Violenjaegar from his prison. And with all the other beings, human and Transformer, who have died on this world over the millenia, Violenjaegar has a near limitless supply of life to draw upon. I fear we face a threat far greater than The Fallen and Megatron combined." I personally think this would work far better than Unicron on the big screen. Violenjaegar is far from the only "other" big bad in Transformers lore, but his backstory with a minor tweak meshes into a Movie setting nicely in my opinion. Plus it means he can summon up evil zombie Jazz to fight the other Autobots.