New Super Mario Bros./World 4-1

With a new world comes new dangers, and the primary hazard in World 4 is poison water. A deadly swamp covers the majority of the levels in this world, and falling in is instant death, even when you're Mega or invincible. In this introductory course, there are also plenty of Scuttlebugs, arachnid-like creatures that hang on webs, as well as an ally who once helped ferry Mario across the water.

Level walkthrough
Go right and hit all of the blocks you see for coins and a power-up. Up a hill ahead, you can see the two enemies that appear very commonly in this level: red Koopa Troopas and Scuttlebugs. Scuttlebugs hang on the ceiling, but will fall down when you get close. The only danger they pose is if you touch their body, but they're often placed above swamp water, so any sloppy attempts to stomp them could result in you falling into the poisonous lake. Koopas are usually nearby to help you defeat the Scuttlebugs from a distance, but fireballs work just as well.

After the first gap, you must deal with another Scuttlebug and Koopa pair. After that is a trio of Scuttlebugs hanging above the ground. You can use these to practice jumping on top of Scuttlebugs, a skill that will certainly become handy for the rest of the course. Across another gap is a Koopa and some Goombas. One of the blocks here contains a power-up. Following this, you have to jump on some fairly thin platforms, with Scuttlebugs between some of them to make the task harder. Soon, you will see a Star Coin hanging in the air. Two Scuttlebugs will drop below it, which you must jump off of and use the bounce that results to collect it.

After the Star Coin is a platform with some brick blocks. Get on the center block and jump straight up to hit a 1-Up block. After that is a pair of Scuttlebugs with a thin column in between. Go past that and over the hill to land on a blue plesiosaur, passing the checkpoint flag as you do. This gentle giant is called Dorrie, who you might remember from Super Mario 64. His hide protects him from the deadly poison, and he will gladly ferry you across the swamp. You must now stay on Dorrie as he moves through the water, dodging or beating Scuttlebugs in your way. Get on the first set of brick blocks and jump off of it once Dorrie moved past you to collect a Star Coin in midair.

Scuttlebugs will continue to fall as you move across the swamp on Dorrie's back. If you're feeling impatient, you can ground pound Dorrie's back to make him move faster. Eventually you should arrive back on solid ground, greeted by two Koopa Troopas. Up the hill, your next challenge are some platforms made from donut lifts, as well as a few Scuttlebugs. The donut lifts are often located above the poison water and will drop if stood on for too long, so make your move quickly.

After making it on to a narrow column, you can see the last Star Coin awkwardly placed in a valley just above the water. Defeat the nearby Scuttlebugs first, then drop on to the Donut Lifts. Dash across the lifts to cross the small gaps between them and get the coin. Jump out of the valley and over another Scuttlebug. Two Goombas will approach from the right. Take them out, jump on to the top of the hill, then leap on to the Scuttlebug and to the flagpole to complete the level.

Star Coins

 * 1) This coin is out in the open, above a pair of Scuttlebugs. Jump off one of them to bounce up to it.
 * 2) The coin is suspended in midair during the Dorrie section. Get on the brick blocks before it, then jump as Dorrie moves below you to land on it safely.
 * 3) Inside a wide valley surrounded by Scuttlebugs and above poison water. Defeat the Scuttle bugs and dash across the donut lifts to get it.

Alternate exit
During the Dorrie ride, wait until you approach the third set of brick blocks, which also happens to be the longest. Get on the brick blocks and stand in the middle. Jump directly up to cause a vine to pop out, which leads to a platform with a pipe in the canopy of the jungle. When you emerge, jump on to the hills and try to leap over the trio of Scuttlebugs to reach the top of the red flagpole.

This secret exit lets you bypass two levels to get to World 4-Tower, granting access to a green Toad House along the way.