What's old is new again.
A homebrew developer by the name of Mico27 recently released a port/"demake" of the original Super Mario Bros. for the Game Boy Color. It should be noted that this project is markedly different than Nintendo's port of the game, Super Mario Bros. Deluxe, which was released in 1999. Unlike Nintendo's version, Mico27's game features tinier graphics intended for the Game Boy Color's screen and is chock full of extra content.
The project is titled Super Mario Bros. Mini. It features the entirety of the 1985 original game, scaled down to better fit on the Game Boy Color's diminutive display. However, all 8 worlds are present, as well as all enemies, blocks, coins, and everything else one would come to expect.
In addition, there are quite a few new features in Super Mario Bros. Mini. Chief among these is a level select option, which lets players select which world and level on which they'd like to start. This is accessible by pressing the B button on the title screen. Players that scroll through the selectable levels will also notice there are 8 additional worlds to play, bringing the total to 16. Additionally, there are extra bosses from Super Mario Land (the first original Super Mario game on the Game Boy) and a new power-up: Yoshi.
Mario's paleolithic pal works similarly to a short-range fire flower. While the dino cannot swallow enemies in this game, his tongue is lethal.
There are some quirks to the title. For one, no more than one projectile (whether a fireball or Bullet Bill) can be on the screen at once. The controls feel a fair bit stiffer than the NES original, and music audio cuts to make room for sound effects quite often. Still, Super Mario Bros. Mini is an interesting and faithful port and feels right at home on the Game Boy Color.
The ROM file is a whopping 2048 KB, which puts it at the same size as Game Boy Color juggernauts like Pokemon Crystal and Wario Land 3. You can download a ROM to play on original hardware here.