MAME4ALL Dingoo currently emulates lots of arcade games supported by original MAME 0.37b5 plus some additional games from newer MAME versions. Some larger games currently do not work due to lack of system RAM.
Or when your player dies, you can say in code, if enemy exists, do nothing, but if enemy does not exist, then create enemy at certain spot. (This would be a pain tho for lots of emeies)