Just keep punching,kicking,ground pounding and jump sliding until he falls into the Hot Boiling Stinky Lava.
fight the end dude
You have to beat world 6
Just beat 5th boss as Mini Mario.
secret exits
You have to beat Mummipokey (the boss of World 2) as mini Mario.
You beat it.
You have to beat the Level 5 castle in mini Mario form.
Beat world five's boss as mini Mario/Luigi.
if you mean new super Mario bros, then you beat world 6 castle when you are mini Mario.
die
beat world one.
beat world 6