Tools and utilities that can read, extract and modify Nintendo DS ROM files on your home computer. Patching software for patching formats commonly used in DS ROM hacks are also available here.
Game/series specific ROM hacking tools, save editors, game specific cheat code creation can be found here too, more general tools (that are not unpacking tools) are in the development section.
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)