--IMPORTANT!!-- I know how to make more than one of each kind of objects aviable at a time. However, there ain't space on the stage to do this.
Sorry for the flash size. Try to find the "secret" button while waiting for the movie to load.
I encourage you to Read the Help text. Just hover over the Help button in the lower left corner. This is slightly different from normal Scenecreators, so don't judge it by the name. You can only have one caster at a time, one melee at a time, one spell at a time and one monster at a time.