Question: nsmb how to get to world 4?
Answer: Go to the final castle level in World 2. World 2 is the desert world. ... 
Get the mini-mushroom. You can find the mini-mushroom towards the end of the castle level. ... 
Get to the end of the level as Mini-Mario. There's another power-up later in the level. ... 
Defeat the worm as Mini-Mario.