Transformers: Revenge of the Fallen

Once you complete the Autobot Campaign, just keep playing the last level over and over again until you get this achievement. The last level will give you 200,000 energon just for beating the level, so any bonuses (like all skill shots) you earn will be added to that. Once I beat the Autobot Campaign, I already had 1.6 million and only had to play the level 2 more times. Also, it takes more then 2 million energon (about 2.8 million) to acquire all Autobot upgrades so once you get this achievement you will be very close to the Power to the People achievement as well.

Don't worry about the credits, you are only forced to watch them once. So the next time you beat the last level you will be immediately returned to the upgrade screen.

The most time effective way to earn Energon in this game is to head over to; Cairo Pyramids - Rise Of The Fallen.

You can just keep replaying the level and defeat The Fallen over and over again, once you've gotten used to the level and what you need to do to finish it you should be able to finish the level in about 3 minutes, which not only will net you the Platinum medal for this level but for defeating The Fallen you'll net yourself 200,000 Energon which is what is used as currency in this game.

It's worth pointing out that this achievement is accumulative, you don't need to have 2 million Energon at any one point to unlock this, so I suggest that while racking up the Energon you work on this; Solution for Power to the People In Transformers: Revenge of the Fallen, doing both achievements at the same time will make completing the level that bit easier/faster.

I've linked in a video of someone playing/completing the last mission (named above), if you find yourself stuck on it or confused about what to do, use it as a reference!

* ^{Credit to captainxena for the video}

After you have completed the last mission on the Autobot campaign you can replay the mission again to earn the remaining energon needed. You can also replay the mission with different characters.

I found by far the quickest way of doing this is to play as the plane, i think he is called Breakaway.

Each sniper shot you fire reduces the Fallen's health a lot more than trying to blast him as Optimus Prime.