New Super Mario Bros./World 4-Castle

Lava returns in this iteration of Bowser Jr.'s castle, with huge platforms installed which swing back and forth over the searing sea of fire. This castle also boasts an impressive Thwomp-filled hallway, with plenty of Thwomps intent on crushing you and even some Super Thwomps that can break through stone. The boss of this World is a familiar enemy, but one on a scale bigger than any you've fought before.

Level walkthrough
There's no difference between lava and poison water, both are lethal to the touch, so you must treat these two liquids with caution and care. The floor is covered in a lava sea, and you must use the large swinging platforms to get across. There are only three in this first section. To be safe, only jump off the platform when it has swung fully in one direction. The last two swinging platforms have Dry Bones on them, as well as a Podoboo shooting out from the lava between them. Wait for the third platform to swing to the right, then jump on to a stone ledge to get the first Star Coin.

Drop down and go right to enter the Thwomp hallway, the main highlight of this castle. Many Thwomps hang from the ceiling, waiting for you to get close so that they may crush you. If you happen to be Shell Mario, you can actually defeat Thwomps with a Shell Dash, as well as the standard Star or Mega Mushroom. Blocks with a cross pattern on them mark the impact site of the Thwomp. After the first three Thwomps, you arrive at a vertical shaft with two different paths. You can either wall jump up the left side of the shaft or use the platforms to climb up the right. As there are coins to the left and a Thwomp at the right, the better choice should be obvious to you.

Up the shaft and proceeding onward, you will come to a Super Thwomp. It is simply a larger Thwomp, and can be defeated the same way. However, its added mass lets it destroy stone blocks, such as the floor below this first Super Thwomp. Have it break the blocks for you, then fall down into the hole to get the second Star Coin. The two "X" blocks above it will protect you from the Super Thwomps fall, but you must still be careful getting out. After that, you must go down a gradual flight of stairs with more Thwomps. Due to the sloped nature of this section, it is better to jump over the Thwomps when they're below than try to run underneath. Evade another Super Thwomp and hop across the lava to trigger the checkpoint flag.

Jump over both gaps, avoiding the Podoboo in the second one. Some more swinging platforms are the only thing between you and the double doors. The one block next to the wall before the swings contains a 1-Up, but it can be hard to grab due to the sea of lava right beside it. Jump on to the first swing and you can see the last Star Coin on a small platform below the swing. As the swinging platform gets fully tilted, jump off of it and on to the small platform to get the coin. Now it's only a matter of jumping across more swings to get to the boss door. Podoboos are the main threat here, since they can easily pop out in the path of a swinging platform.

Boss: Mega Goomba
Mario can turn Mega, but so can his most commonly killed enemy, the Goomba. Bowser Jr. has found out how to use the Mega Mushroom on his own troops, and he's trying out the first Mega Goomba on you! The Mega Goomba behave much like a standard Goomba, but it will charge at you if it spots you. It's hard to avoid, but there are small spaces in the ground to duck into if you're cornered. It is not only immune to stomps, but also fireballs. The primary way to defeat it is by hitting the switch at the center of the arena, which causes two rising platforms to appear on either side of the arena. Use the platforms to get some height, then flatten the oversized minion with a ground pound. Do this three times to defeat the Mega Mushroom. Using the Shell Dash as Shell Mario also hurts Mega Goomba as well.

Bowser Jr.'s mega-sized plan has failed, and he is forced to retreat further. Your next destination is World 5, a cold and snowy wonderland. The difficulty will really start to pick up, so stay vigilant.

Star Coins

 * 1) On the last swing platform before the Thwomp corridor, wait until it swings to the right. Jump off the swing and land on the stone ledge to get this Star Coin.
 * 2) Have the first Super Thwomp destroy the blocks below it. Fall into the gap to get the Star Coin.
 * 3) This coin is right below one of the swinging platforms in the latter half of the castle. Hop on to the thin platform the Star Coin rests on once the swing is fully angled.