The Easy Way To Kill The Fallen
The easy way to kill the fallen is when he's throwing pyramid pieces at you go behind the alien ship looking thing then grab it and push it till you get closer to him then after you get to him he'll start stomping fire then start shooting him then he will shoot a slow fireball stand right in front of a portal then right when the fireball is about to hit you, move away then it will hit him keep doing this till a video pops up then you will go up higher then right when he stomps fire jump then hit him three times, keep doing this until you kill him.
Defeat Megatron In Desert
First use circle to block that is helpful but the main thing is to use your secondary weapon by pressing L2 hold it down so you charge it then release L2 button then he will get shielded then kill the minion then do the same again and then then defeat the two minions then blast megaton. Then kill the two minions again and that will be the last time.