JumpJet Rex Easy “Fat Stacks” achievement
Play the “Scrollway” level and enter the hidden bonus level. It can be found after the laser section. Drop through the hole in the floor and stand on the glowing platform. After you are in the bonus level, fly through the first row of coins to increase your multiplier to 4x, then reach the end of the level all the way to the right and collect the ruby. Note: Watch your multiplier, as it decreases rapidly.