Foot stomp 12 aliens

In order to get this trophy/achievement you have to stomp on 12 aliens making them die a squashy death. The main aliens that you can kill by stomping on them is Octobabies, but you will also be able to do it on other shrunken enemies later in the game. To stomp an alien to death, simply look down at it and walk over it. The first level you will be able to do this is in "The Hive". This Chapter contains a lot of Octobabies, so just keep stomping every possible alien in this Chapter and the trophy/achievement is yours.

Later in the game, in "The Duke Burger", you will find your first Shrink Ray on the rooftop. If you haven't got the trophy/achievement yet this gun is great for getting some more foot stomp kills