How do I check if all instances are destoryed?

I'm testing out an rpg combat system,and managed to get it working,however,I wanted to add more than one enemy,and cannot figure out how the make the game detect if all enemies are destoryed to change the state.

You can check if Enemy.count=0

If you are adding new enemies, consider using a family for them.

Thanks for the info. Also I think families are subscription only,so I can't use it.