How to make a mob spawn others in another position

I'm working in a GPQ script and now i got a problem in 4th stage when you have to kill the monster on the top and then it spawn some mobs in the ground bellow, so you can kill and get the drops. How can I make the monster spawn others in the ground bellow when he dies?
This is the monster:
http://www.mapletip.com/maplestory-m...rgoyle/9300025