Mario and his brother Luigi have been tasked with cleaning out the critters that have infested New York City's sewer system. They quickly discover this is easier said than done! There aren't any big apes down here, but there are plenty of other critters spilling out of the pipes, ready to make life difficult for our heros. Will you help them?
Mario Bros. is for one or two players. Each player controls one of the Mario Bros., running and jumping to clear each level of its infestation. Up to three different kinds of pests appear in every level. Shellcreepers meander lazily across the platforms. Sidesteppers move more quickly, especially when provoked, while Fighterflies hop across the platforms. To kill each pest, Mario or Luigi must jump up and bump the platform directly underneath as it crawls past, flipping the critter on its back. Next, Mario or Luigi must hop up onto the same platform and knock the pest off the platform, before it has a chance to get back on its legs. Shellcreepers are the easiest to dispatch, requiring only one hit to flip. Sidesteppers are more challenging, requiring two hits, and moving faster after the first hit. Fighterflies take just one hit, but they can only be flipped while they are touching the platform. Any pest that is allowed to flip back over will move even faster than before. Don't dawdle!
A certain number of Shellcreepers, Sidesteppers and Fighterflies must be killed to clear each level. Other enemies will also appear during this quest. Green and blue fireballs zip left and right over the platforms, toasting any plumbers in their way. Orange fireballs zig-zag over the platforms, bouncing back whenever they reach a platform or the edge of the screen. Later on, Slipice also appear, crawling out of the pipes along with the other pests. If a Slipice isn't killed quickly, it will coat the platform under itself in a thick sheet of ice, making it even harder to move! Fireballs and Slipice can be killed if you bump the platform underneath at just the right time, but once they have appeared, they will always come back until the level is complete.
Killing a Shellcreeper, Sidestepper or Fighterfly makes a bonus coin appear. If Mario or Luigi can grab these coins before they rolls into the pipes below, the plumbers will earn even more points. But don't let them get so focused on coins that they run into a critter that hasn't been flipped over! Every so often a level will contain nothing but coins, hanging from the platforms instead of rolling across them. Here Mario and Luigi can grab coints to their hearts' content, and will even score extra bonus points if they collect them all before the timer runs out.
In the middle of the screen is the POW box. If Mario or Luigi hits this box from below, every fireball and coin will disappear, scoring points for the player who hit the box. Also, every Shellcreeper, Sidestepper, Fighterfly and Slipice touching a platform will register a hit as well. This may be enough to flip them over (remember, Sidesteppers need two hits), but it will also flip again any critter already on its back! Be careful how you use the POW box, because it can only take three hits before it disappears. The POW box is replenished at the start of every bonus level.
Later in the game, the last enemy will appear, icicles, hanging off the highest platform and the pipes above, before breaking off and plummeting downward. At this point the Mario Bros. must kill pests and avoid all kinds of enemies, both hot and cold. Good luck!