Chapter 5: The Final Guardian
Megatron vs. The Omega Key
Objective: Destroy Omega Supreme's Turrets
AUTOBOT symbol: At the start of this battle, there should be 3 Autobot symbols that can easily spotted. The easiest one to locate is the one in the “pit” where Omega Supreme is standing. It is beside an Overshield upgrade. Make sure to destroy it quickly and get the Overshield before the guardian hits you hard.
AUTOBOT symbol: For the second symbol, head to the highest platform in the area and turn around. You should see the symbol under an arc overhead.
AUTOBOT symbol: As for the third, you'll need a scoped weapon, preferably the photon burst rifle found in the same platform. If you're facing Omega Supreme, look to the left to find a different structure as shown in the screenshot. The symbol should be in the middle of it.,
There are six turrets in total; two turrets on O.S's shoulders (front and back) and two in his torso. Use the walls for cover while you take those turrets out.
Objective: Corrupt the batteries to defeat Omega Supreme
After taking out the turrets, the second phase of the battle will start. O.S will routinely absorb energon batteries that are supplied by fixed terminals in the battlefield. The task at this point should be easy; inject dark energon into the batteries to corrupt O.S and render him vulnerable. O.S will turn purple while he attempts to purge the dark energon. During this point, unload all your ordnance unto him. Exhaust both weapon ammos or better yet, pummel him with your cannon in vehicle mode. He will occasionally release flyers to annoy and distract you. Just remember that you should prioritize injecting the dark energon into the battery when its up. Repeat this process until he falls and to start the final phase of the battle.
Omega Supreme's Last Stand
Objective: Destroy armor protecting Omega Supreme's chest
He'll be more aggressive and will continuously attack you. As much as possible, stay away from your teammates as they'll serve cannon fodder and distraction while you do your stuff. He can easily destroy objects during this form so you can easily get the last two remaining symbols. Also, you can have him destroy all cover/ barricades in the arena to unlock the “Devastator!” achievement.
AUTOBOT symbol: On the highest platform, have him destroy the barrier to the left. The fourth symbol is hidden inside.
AUTOBOT symbol: As for the last symbol, you need to have him destroy one of the arcs in the hallway to the right. The symbol is affixed up in the wall.,
There is a turret platform in the highest point of the combat area. Be careful not to detach this unless its really necessary since this is one of your best tools to deal considerable damage to O.S armor plate. Alternatively, you can also attack using your vehicle cannon. Keep doing this until he ultimately falls down and for you to officially complete the Decepticon campaign.