Here is a hack for Mario Bros which changes all the graphics in the game and gives it a new hero to play as with new drawn enemies.
Mario Bros. (World).nes - NOINTRO
CRC32: A6DE1B55
MD5: 8D8E0B86DD870302BF4A994E76C55C83
SHA-1: 9286A2DB471D51713E9B75E68B47FFBF11E2D40B
SHA-256: 2810051C21132ABD8B9B1E1BF741B302EE6C1D4AF983E0DF7FE50BD05AC0A5C8