Just when you thought that Bowser and his Koopalings have already learned their lesson about messing with the Mario Brothers, they are already at it again. The only difference is that Bowser is currently wreaking havoc in the Dinosaur World. Now it's up to Mario and Luigi to rescue Princess Toadstool, save Dinosaur World and hopefully put Bowser and his Koopalings in their place.

The gameplay action is sidescrolling as in previous Mario games and it takes advantage of the SNES's 16-bit graphics and stereo audio. The game consists of a journey through levels in seven worlds: Yoshi's Island, Donut Plains, Vanilla Dome, Twin Bridges Area, Forest of Illusion, Chocolate Island, and the Valley of Bowser. There are also two secret worlds--Star World and Special World (accessed via the Star World)--which can be found by completing secondary goals in specific levels.

SMW contains a map screen on which the player moves, expanding this concept which was introduced in "Super Mario Bros. 3". It features 72 courses laid out across the seven worlds, and 96 exits (some levels have more than one exit). Secret exits open up new routes on the overworld map, often leading to secret levels. If you get all 96 exits you can play in a slightly different world.

The Yoshis appear in 4 different colors (green, yellow, red, and blue), each with slightly different abilities. There are also Baby Yoshis in the Star World levels which can be picked up by Mario. After eating five enemies, three berries, a Super Mushroom, Fire Flower, Starman, or Cape Feather, they will become a fully grown Yoshi of the same color.