As said in the other solution, you just have to beat the last checkpoint on EACH of the five Decepticon chapters. This makes it not too difficult, as you do not have to play the entire campaign and they're stackable with the normal and easy ones as well. Good luck!
By far the easiest because you face a bunch of cannon fodder, with two guys carrying turrets at the end. I recommend Megatron for this one just because two shots of his fusion cannon take out all the easy guys. Use his energy drain to suck the life out of the turret guys.
You can be any of the jets, it doesn't matter because you have to be in jet form to beat this level. Energon cubs are in destructable crates on the base of the boss. You won't be able to hurt the boss til he recharges, when you see the energy ball emerge. Just dodge the rockets and the pink energy beams. Using the machine gun ammo first, then switching to rockets rather than wait for a reload, it only took two reveals of the energy ball to take the boss down.
I struggled a bit with this one. Since there are no energy cubes in here to restore your health, it will be very hard if you play as Soundwave because he has the repair ray. When I switched to Megatron, I got it in my first try. Just remember, boost away when the floor is orange, and with the clones spin their staffs, jump so you don't get shocked and slow down. Megatron's fusion cannon will take them down in two shots, his tank gun in one. Drive around a few times so the clones cluster around your buddies and take down multiple ones. Don't forget your ability to hover, it will increase the damage, and just put you out of range for the clone's attacks. When the energy ball emerges, just time your shots. Shoot at the spinning shield and by the time it gets there, it will hit the ball. Two times of this and you're done. Just remember, after Megatron mentions Zeta's boasting, the clones come AND pillars will randomly fall, so pay attention to the floor. Don't forget to use your energy drain on a clone if you need health during the battle as Soundwave will be preoccupied. Ammo, weapons, and grenades spawn where the clones die too.
While taking on Omega in jet form, you have bullet turrets to use in the front and center, and rocket turrets to use in the back up top. Omega seems to forget that you're at the back turrets, so stay up there attached to the rocket turret. His sweeping yellow ray doesn't go up there, but some orange rockets do. They don't cause too much damage though. When he puts his shield up and fires the huge rockets, stay put and just shoot any that come to you to blow them up. After Breakdown whines a bit, and Soundwaves say Omega's defenses are down, Omega will release a few jets. Use the turret to knock them out. After all jets, or all but one, are dead, Omega will return. Same thing as before, some orange rockets, yellow ray, shield and missles, and then jets. Just keep at it, it takes awhile. If you need health, there's respawning cubes on the map, and some energon gernades were behind the right turret that I was using.
Select Soundwave to take advantage of his ram boost as a truck to escape Omega's fire on this level. Whiles Omega is rechaging, grab some ammo, and right by the single wall cover, there will be a turret to activate. Get it as soon as you can and remove it. There is one up top on the other side as well, do the same. Stay away from your comrades and Omega will focus all fire on them, leaving you free to unload on Omega's chest. Just watch the missles that he launches out of his back, they can go in any direction, he does not have to be facing you. Just transform, and zip away to the other side when you're getting attacked and use the turret again. Turrets and energon cubes respawn in this chapter as well which makes this process much easier.
You can also get the Devastator achievement too by having Omega destroy all the cover or walls that you hide behind in the level. Go for it if you're feeling confident, and don't want to play the level again, or just do that one on easy.