Transformers: Revenge of the Fallen

You will not receive this achievement if you receive a superior medal (Platinum, Gold, or Silver). Medals are awarded solely on a target time.

To receive a Bronze Medal simply wait until the Silver medal time has expired, and then complete the mission. On most missions you'll need to intentionally wait this long.

This achievement doesn't stack, which means you can't score yourself a Platinum Medal and get all the related achievements, you actually need to score each medal for each achievement. This may be a pain but it's not hard to do, the easiest method is to use one of the race-to-the-finish style missions.

What you want to do is play through the mission like normal and when you reach the end just wait it out until you'll finish on a Bronze, then do the same mission and repeat what you did last time except finish for a Silver, then again for Gold and then once more for Platinum. That being said you can do this in whatever order you want, once you've scored Platinum your mission ranking wont be affected but you can still unlock these achievements on that mission!

I've linked in a video which shows you how to get a Platinum medal on the first available race style mission on the Decepticon campaign, you may find you need to upgrade your character a little in order to get Platinum, if after upgrading you still can't do it, keep trying, you will eventually, especially with the video showing you how! Of course if you really can't get Platinum on the level in the video you can always try another!

* ^{Credit to Flickffxi for the video}