Supersonic Wii is a rhythm music game for the Wii, in which you have to press the correct buttons in tune to the music, similar to the PS2 game Amplitude. The game supports using a Guitar Hero guitar. See the video for a demonstration.
I don't have a wii u anymore to test it myself, but if homebrews are not visible on the wii u menu I think you can press L + R + minus to open the plugin menu, there should be an option called "homebrews on wii u menu" or something similar
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)