In this video guide I will show you how to find the hidden green gem. It will be located on the map The Hazardous Wastes
in the the level Hit the Road
. You will need to get to the part of the level where N. Gin is chasing you in a ball. Once you reach the checkpoint and get out, you will need to melee the trash can on the left. Then the remote on the right, and the car in the back. This will destroy the nitro crate next to you and reveal the green gem. Grab it and finish the level and the achievement will unlock.