World 6 (New Super Mario Bros.)

Mario & Luigi, after defeating Petey Piranha, traveled on to World 6. It was a world in some mountain ruins, though some levels were in different terrain. It had 2 towers but no ghost houses. The castle, at the end, came after a level infested with Chain Chomps, Koopas and Warp Pipes.

The boss is Monty Tank, and he fires Bullet Bills at Mario or Luigi. He may pop out to throw a Bob-omb into the mix.

Enemies introduced

 * Deep-Cheep
 * Chain Chomp
 * Mega Deep-Cheep
 * Firebar