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World 4 is a secret world in New Super Mario Bros.. If Mini Mario or Mini Luigi defeat Mummipokey in World 2 they will go to World 4 instead of World 3.
World 4 is a giant forest with many enemies like Wigglers. Also, much of the water here is so polluted that it eminates an eerie purple color and grants instant death, regardless of what form Mario/Luigi is in (even in Mega form). Bowser Jr., like in every world, is fought here, and a Ghost House is also located here. Mega Goomba is the big boss of this world.
4-1
In this level, strange purple goop covers the ground. If Mario touches it, he will instantly lose a life. To start, Mario should keep walking until he finds some Scuttlebug. He should jump on them to gain a jumping boost, which is used in collecting the first Star Coin. About halfway into the level, the player should see a Dorrie. Jump on it to ride it, while avoiding the Scuttlebugs. To get the second Star Coin, Mario again should get a jumping boost from the Scuttlebug. After getting off Dorrie, Mario should jump onto the donut lifts to avoid falling into the goop. The final Star Coin can be obtained by using a Koopa Troopa and throwing the shell at the coin. After this, Mario reaches the Flagpole.
Secret Exit
While Mario is riding Dorrie, the player should notice that on the way, there are two ? Blocks with three normal blocks in between. If Mario gets on top of them and jumps in the middle, a Beanstalk will appear. Climb on it and enter the pipe to reach the Red Flagpole. The secret path opens up a Toad House and takes you to 4-Tower.
4-2
This level has purple mushrooms that, when Mario stands on them, tilt to the side he's on. Move quickly to avoid falling off of them. The first Star Coin can be obtained by Wall Jumping to it. To get the second Star Coin, Mario must let one of the purple mushrooms tilt to the right. Once the player gets it, jump off to the next mushroom. Soon after the coin is a Red Coin Ring. Mario will come to a stepped platform. Jump on the purple mushroom after it, let it lean to the left, and jump over to the brick and hit it to reveal a Beanstalk. Climb it to go to a bonus area. Go up to find the third Star Coin. Then the player should go through the Warp Pipe and get to the Flagpole, ending the level.
4-3
4-Tower
4-4
4-A
4-Ghost House
4-5
4-6
4-Castle
The player will start off on a ledge. They will see a platform that will swing from left to right, along with a ? Block containing a coin. The player will see coins floating in the air, aswell as another ? Block, this time containing a power-up. The player will now have to jump on another swinging platform, which will have a Dry Bones wandering on it. A Podoboo and another swinging ledge with a Dry Bones can be seen. If the player jumps when the swinging platform is at it's max height, they will get their first Star Coin. The player will fall down, and see a Dry Bones along with two ? Blocks, containing coins. Now the player will see a couple of Thwomps. The player can take two routes from here, either Wall Jump while collecting coins, or jumping from platform to platform while avoiding a Thwomp. In the lone platform, there is a Hidden Block with a Star inside of it, along with two visible one's containing coins. The player will see a couple of Dry Bones and a Super Thwomp. If the player waits while the Super Thwomp is crushing the blocks, they can get their second Star Coin. The player will find a ? Block, containing a power-up. The player will meet up with more Thwomps and Dry Bones, aswell as another Super Thwomp. The player will collect some coins and find a Dry Bones here. The player will now be at the checkpoint area, and see a ? Block containing a power-up, a Podoboo, and another ? Block which will have a 1-Up Mushroom. The player will be on a swinging platform, and see their last Star Coin.. The player must jump from the swinging platform to another, while avoiding a Dry Bones and many Podoboos. The player will now see a boss Door, and will fight Mega Goomba. After the player has defeated it, they will now have access to World 5 (NSMB).
Enemies Introduced