Instructions
Explore every area thoroughly. Gremlin cages and chests are often tucked away under tall objects, placed on high platforms and hidden behind walls that you can get rid of using Thinner.
Look around the surrounding area if you find a Gremlin cage or chest but can't figure out how to get to it. Although most Gremlin cages can simply be approached and destroyed, some require additional actions before you can access them. For example, to free one of the early Gremlins, Calvin, you have to use the nearby catapult before you can reach him.
Hit the Gremlin cage with your Spin Attack to break it open. When you do this, the Gremlin will be free and may reward you with a pin or other item.