Reach the secret room where you get the Alchemy Coin in the "Explodatorium" level. This room has six enemies in a narrow corridor at the bottom, with a lone Greenarmor above. Cast the Mobile Gear down there, jump on it, then allow it to crush all the enemies. Note: You do not need to ride the Mobile Gear; just jump on it so that it activates. Consider waiting until all the enemies are on one side before using the relic for best results.