World 4 is called Big Island. Here, you'll find out everything has become giant! This includes not just the terrain, but also the enemies, so take special care here.
You start off on a small part at the left which is connected to the island with pipes. The map contains multiple pipes which have been colored here, pipes with the same color connect together.
If you didn't use the Hammer from World 3 (or from World 2, for that matter), go through the pipe at the beginning and use the hammer to break the rock to the left. You then gain access to a special red mushroom house which contains a Tanooki Suit! The two normal mushroom houses here feature the standard mushroom, leaf, flower choice. There's another red mushroom house at the top left, it allows you to choose between a leaf, a flower and another Tanooki Suit.
This map has Sledge Bros. patrolling. They are similar to the normal Hammer Bros., but can stomp on the ground to stun you, so jump in the air to avoid this.
4-1
This level is no different from the World 1 levels other than the giant enemies. If you're Raccoon Mario, you can fly up a waterfall pipe and enter a water room for 1-Ups.
4-2
Like 3-3 and 3-8, this level rises and falls. If you get 22 coins, you'll get a White Mushroom House visit!
4-3
This level starts with Sledge Brothers, the giant kind of Hammer Brother. After that, enter the Pipe and you'll be in a cave with Buzzies and Spinys.
Fortress
This fortress has horizontally moving Thwomps and a new kind of enemy, Hot Foot. When you come to the set of 5 pipes, there is either the option of getting by them and continuing to Boom Boom's room, in which case there's one Thwomp that you're going to have to duck to get past by, or entering the third pipe and going underground. In the latter case, you'll get to Boom Boom's room after exiting the pipe.
4-4
This water level has a Lakitu! If you're Frog Mario, you can enter an exciting coin room by heading down and just to the left to find a pipe. If you want to get to this pipe without a Frog Suit, you'll have to do a special technic by floating off a ? block with a Fire Flower. (Variant: In Super Mario All-Stars, the water is lower in the beginning of the level, but higher after the wall. As a result, it is more difficult to get to this secret room without a Frog Suit.)
4-6
This level has doors that change between two versions, giant and normal-sized. There are also a few other differences between the versions.
Giant sized
This is how the level starts. In the rectangle of bricks, a 1-Up appears. The ? just after the door contains a Raccoon Leaf. Later in the level, there are 3 invisible bricks, all of which contain coins.
Normal sized
Entering a door will switch you between the versions of the level. In normal-sized mode, if you go to the left and see the same rectangle, it will contain a Starman. The ? just after the door contains a coin, and the 3 invisible bricks contain 2 coins and a 1-Up. Entering a door will take you back to the giant version.
4-5
Located in the middle of the level is a brick that you can break to get a green Vine. You can stomp on a Bullet Bill to reach above the brick to climb the Vine and get a Tanooki Suit! After getting it, get the P-Switch and exit the pipe, collecting the coins as you fall down until you reach the end.
Fortress
Be very careful early in this fortress; the platform is made of doughnut lifts. After a while will be a brick containing a P-switch. After getting it, you'll see some new coins surrounding an invisible doorway taking you to a secret room. Enter it and you'll notice a pipe maze where you can ride lifts, some of which can change direction, others cannot. At the top is a pipe taking you to a secret room with 9 coins and a 1-Up, and after that is another secret room with a large block with 3 1-Ups! After exiting the pipe, you can get to Boom Boom's room.
Airship
The king has been transformed into a dinosaur. All the cannons are Rocket Engines, and this ship has the Bolt Lift, which you can jump on several times to ride. At the end is a pipe that leads to Iggy Koopa, who you can stomp on 3 times and get a wand. If you kill Iggy and you still have the Tanooki Suit from 4-5, you'll get the message "Thank you kind raccoon, please tell me your name!" from the king. You'll get a message from Princess Toadstool with a P-wing.