Transformers 2, Revenge of the Fallen

     Transformers, Revenge of the Fallen is the second installment in the live action movie saga. This movie was more successful than its predecessor in the box office. It picked up 2 years after the events of the first movie.  

    The Autobots joined the military, hunting down the remaining Decepticons on earth. In the backround, the Fallen (banished prime) sent out Depticons to find an ancient machine which harnesses the power from the sun. In order to do this, the Decepticons need the matrix of leadership as its key. During a battle between Optimus prime and the Decepticons, the Autobot leader was killed. After the primes' death, Sam and some of his allies set out to find the matrix.. On their journey, they find an ancient Autobot that knew the location of the matrix. Sam finds the matrix but it turns to dust when slightly touched. For some reason, the military bring Optimus prime to the desert, where the matrix magically reintegrates itself and Optimus is revived. after the matrix regains its form, the fallen uses it to activate the machine and harness all the power of the sun. One Optimus has regained his strength, he brutally kills the fallen, deactivates the machine, and the Decepticons run away cowardly.

TL,DR, Optimus dies, comes back to life, and kills the Decepticon leader. Same formula as the previous film but with a bit spicier action scenes.

Here is the wiki page of the movie. This should help you understand the movie in more detail if you are interested

 https://tfwiki.net/wiki/Transformers:_Revenge_of_the_Fallen_(film)