Despite what the name implies, Wacky Races for NES is not a racing game, and has nothing to do with the other games bearing the same name but the license. In this game, the player takes control of Muttley, the grumbling, but loyal dog from the popular Hanna-Barbera cartoon. His master Dastardly sends his on three different missions, each taking place in a different location, which in its turn is divided into smaller levels.

Muttley has to complete those levels in a rather standard platformer fashion, moving from left to right, jumping, overcoming obstacles and fighting various creatures and boss enemies from the cartoon movie. The dog's primary weapon is, unsurprisingly, his own mouth - biting regular enemies will usually lead to their instant death. Muttley can also collect bones scattered across the levels, which will grant him powerful weapons and skills of limited use, such as a bomb, a projectile attack, and the ability to heal.