Would this be a sub event? Since this happens after the enemy dies. I'm a bit confused on how to make this happen. Should I make two Global Variables, which is what you mean by Compare two variable?
I apologize, I just need more clarification.
Event: Enemy: On Destroyed.
Sub Event: System: Compare two values: random(100) less than 60. Action: Enemy: Spawn Another Object
So when an enemy is destroyed the sub event check is triggered. Then the game rolls a random number between 0 and 100 and if the number is less than 60 the check returns as true and the action following it runs. If the number is 60 or above the check returns as false and the action is not run.
If you want to be able to change what the number is checked against you can create a global variable. Then your action becomes: Compare two values: random(100) less than GlobalVariableName.