New Super Mario Bros./World 4-2

It seems like the poison swamp is not only dangerous to plumbers, as it has bizarre effects on mushrooms as well! In this athletic level, bright purple mushroom platforms tilt steeply when you step on them, turning what looks like safe ground into a precarious obstacle. Stay jumpy to avoid falling off, as there are plenty of pits to fall into.

Level walkthrough
The level starts with the usual stationary mushroom platforms and one lone Koopa Paratroopa. There is a set of blocks here, one of which contains a power-up. Move right to come to the first example of a purple mushroom platform. These sickly looking mushrooms with bright orange spots have very weak stems, and they will slant steeply in one direction when you stand on them. The angle is so extreme, you will simply slide off if you stay on the platform. You can prevent the mushroom from slanting if you stand at the center though.

After going across a long red platform, you will have to jump across three consecutive purple mushrooms, some with Goombas on them. Once you fall on to the green platform, hop to the next purple mushroom, being careful with the red Koopa, and hop to the red mushroom platform. You should see a small crevice with a Goomba roaming inside. The leftmost block in that section contains a 1-Up. Ground pound it and fall down, then attempt to grab it before it falls into the pit. The purple mushroom platforms here are wider, so you'll need to jump very often to make them move back to a balanced position, letting you move slowly across. Once you see a Star Coin, jump off the nearby wall to get it.

The block below the Star Coin is a 10-coin block. Ground pound it to get all of the coins within. Afterward, fall to the red mushroom platform to trigger the checkpoint flag. Hop on to a thin purple mushroom, then quickly to the next purple mushroom, one with a red Koopa on it. There is a Star Coin hanging below this platform. Make the mushroom tilt to the right and slide down just enough to collect it, then jump up to the green mushroom platform. Soon after, you should come across a red ring. The red coins it spawns are located close to each other, and all but one does not require any intentional mushroom tilting to get.

After the red coins, you will get to an irregularly shaped stone formation. Jump off of it and move to the left to land in the crevice below it. Collect the coins here, then bump into the brick block from below. This causes a vine to pop out, extending into the sky. Climb up it to reach a bonus area with a lone brick block. Hit that to make another vine come out, which takes you to a cloud platform high in the sky. Jump to the left to nab the final Star Coin in the level. Exit the bonus area through the warp pipe. Go right and leap across the last few purple mushrooms to get to the flagpole.

Star Coins

 * 1) The coin is plainly visible, high in the air. Wall jump off the stone wall to the left to reach it.
 * 2) This coin appears soon after the first. Tilt the purple mushroom platform to the right and quickly grab it before jumping off.
 * 3) When you reach a large stone platform with a lone brick block in the floor and some coins in a crevice underneath, get below the brick block and hit it to make a vine extend. Climb up the vine to head to a secret area, then hit the block there to make another vine, one that lets you get the coin.