This hack that adds difficulty. There are many bosses as well as enemies to make it challenging and interesting.
Database match: Double_Dragon_2-The_Revenge.nes
Database: No-Intro: Nintendo Entertainment System (v. 20180803-121122)
File SHA-1: E4FBBE69B3B539B198AE0E037FDC2558074A283F
File CRC32: A0F7027D
ROM SHA-1: 5BF8F3D23F0819E23B9BCC9F1DFAFD3B6106C4F2
ROM CRC32: 8A640AEF