The player takes the role of Mario, or in the case of a second player, Mario's brother Luigi. The ultimate object is to race through the Mushroom Kingdom, evade or eliminate King Koopa's forces, and save Princess Peach (or "Princess Toadstool" as she was commonly known in North America until 1996). Mario's primary attack is simply jumping on top of his enemies, which kills the mushroom traitors, known as Goombas, and sends the turtle soldiers known as Koopa Troopas into their shells. Mario can then kick these shells into other enemies, which will conveniently dispatch them; but conversely, kicked shells can bounce back off walls or other vertical obstructions and hit him. Jumping on enough enemies in succession or kicking a shell into enough enemies in succession (combos) results in double points earned with each enemy killed, eventually earning Mario a 1-up, an extra life and another chance to pass the level. Some enemies, though, such as Spinies, can be killed only by fireballs or shell impact; stomping them will hurt Mario.