Today I am trying to remove the key chain off my mini figure. But not successful. Thus I surf around and found that there are a few ways. The details can be found here.
There are three ways:
1) CUTTING OFF THE METAL LOOP: This is one of the easiest methods among the three. All you need to do is to get rid of the metal loop sticking out of the head of the minifig. Simply use cutting-pliers to snip the metal loop off as close to the top of the head as possible.
2) REMOVING THE PIN BY FORCE: Remove the original chain from the loop on the minifig's head. Then, attach a heavy-duty paperclip to the exposed loop on the minifig’s head. Grab the paperclip with pliers with one hand, and the minifig’s body with the other. Finally pull the pin out of the minifig’s head.
3) USING A SOLDERING IRON: This is the fastest method among the three. All you need is a basic soldering iron. The soldering iron has a heated metal tip to melt and weld metal parts together. But got to pull once you find the pin is going to release or else it will melt the plastic.