In the game Mario Bros, Mario is portrayed as an Italian-American plumber along with his younger brother Luigi.
Their aim is to defeat creatures that have been coming from the sewers below New York City. The gameplay focuses on Mario's extermination of them by flipping them on their backs and kicking them away. The original versions of Mario Bros.—the arcade version and the Family Computer/Nintendo Entertainment System (FC/NES) version—were received positively by critics.
Mario Bros. features two plumbers, Mario and Luigi, having to investigate the sewers of New York after strange creatures have been appearing down there. The objective of the game is to defeat all of the enemies in each phase. The mechanics of Mario Bros. involve only running and jumping. Unlike future Mario games, players cannot jump on enemies and squash them, unless they were already turned on their back. Each phase is a series of platforms with pipes at each corner of the screen, along with an object called a 'POW' block in the center. Both sides of every phase feature a mechanism that allows the player to go off-screen to the left and appear on the right and vice versa.
The player gains points by defeating multiple enemies consecutively and can participate in a bonus round to gain more points. Enemies are defeated by kicking them over once they have been flipped on their back. This is accomplished by hitting the platform the enemy is on directly beneath them. If the player allows too much time to pass after doing this, the enemy will flip itself back over, changing in color and increasing speed. Each phase has a certain number of enemies, with the final enemy immediately changing color and increasing its speed.
There are four enemies: the Shellcreeper, which simply walks around; the Sidestepper, which requires two hits to flip over; the Fighter Fly, which moves by jumping and can only be flipped when it is touching a platform; and the Slipice, which turns platforms into slippery ice. When bumped from below, the Slipice dies immediately instead of flipping over.
The 'POW' block flips all enemies touching a platform or the floor when a player hits it from below. It can be used three times before it disappears. In the Super Mario Bros. 3 in-game Player-Versus-Player version of this minigame, each of the three uses causes the opponent to lose a card and all the enemies to be flipped over. Another feature in this small remake is that the pipes are straight, occasionally spitting out large fireballs at the two plumbers. Coins appear whenever enemies are defeated and may be collected for bonus points.
As the game progresses, elements are added to increase the difficulty. Fireballs either bounce around the screen or travel directly from one side to the other, and icicles form under the platforms and fall loose. Bonus rounds give the players a chance to score extra points by collecting coins without having to deal with enemies; the 'POW' block regenerates itself on each of these screens.