Super Mario Bros.: Bullet Bill in Super Mario Bros.

This is a ROM hack that replaces Mario and Luigi entirely with Bullet Bills. As so, there are pros and cons to this. Pros being that you have better jump height, fireballs go straight at tall enemies and you're invincible for longer amounts of time. Cons being that you're slow, even slower in water, you start with only one life and lack the ability to gain much momentum, making it difficult to get high up on the flag pole from the staircase alone. As such, this hack is only for Super Players.

Database match: Super Mario Bros. (World)
Database: No-Intro: Nintendo Entertainment System (v. 20180803-121122)
File SHA-1: EA343F4E445A9050D4B4FBAC2C77D0693B1D0922
File CRC32: 3337EC46
ROM SHA-1: FACEE9C577A5262DBE33AC4930BB0B58C8C037F7
ROM CRC32: D445F698