Here is a hack which replaces the normal enemies with the bosses making the game more challenging to progress though.
Update: Patch was incorrectly created using a US ROM instead of JP ROM. It has been updated.
File Name: Double Dragon II - The Revenge (J).nes
ROM CRC32: A66596D9
ROM SHA-1: 3CC786F4B1B1E884354106793CE0A1159796C3D3
No-Intro entry: Sou Setsu Ryuu II - The Revenge (Japan)