NUS Downloader, or NUSD, is a PC Utility designed to allow easy access to the resources present on Nintendo's Update Servers. Using this tool, you can download, pack, decrypt, and manipulate many system titles into WADs ready to install.
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)