This is the Ice World. It is big, with 10 levels and 3 fortresses!
6-1
This level has Ptooies, which can be killed with a Fire Flower. If you have a P-wing, you can fly and enter a door containing bricks that can turn into coins with a P-switch.
6-2
A side scrolling level with cloud-like elevators.
6-3
At the beginning, there is an elevator that you must duck if you're big if you want to get past it. Later in the level is a white Vine that leads to a pipe with a Tanooki suit!
Fortress
Stay on the elevator throughout the ride. After entering the door, you'll enter a room that you must duck in several spots to get past. The door at the end will take you to Boom Boom's room!
6-4
This has an unusual elevator ride that will have a pink jump block that jumping on will take you to a sky room similar to the one in 3-7, except that it ends with a pipe leading back to the main part of the level.
6-5
This level is best with a P-wing. The exit of the level is not at the very end, but in a location that you must take a Troopa shell up with you to kill the Nippers and break the bricks, and then you can get to the goal panel. In addition, the Toad's House next to this level contains a new item, a Hammer Suit!
6-6
If you have a P-wing, you can just fly over the wall and get to the Goal Panel. If you don't want to do this, however, your best friend in this level is a Fire Flower. You can kill Cheep Cheeps and Piranha plants in this level with fireballs and this level is water in the middle.
6-7
A side scrolling level. Just before the goal panel is a group of frozen coins that you can get only if you're Fire Mario.
Fortress
This is the true icy fortress! It has side-to-side moving Thwomps, but you can kill them if you're Hammer Mario, as well as Boo Diddlies, but not Rotodiscs. There are no secret rooms in this fortress, but the door will take you to Boom Boom's room.
6-8
The only level in this world that departs from its usual Icy climate.
6-9
Another level that you can fly over the wall and get to the Goal Panel with a P-wing. If not, a Frog Suit is good for you. Enter a pipe to get to a coin room. After the pipe, go to the area above and find the entrance pipe.
6-10
Your best friend in the first half of this level is definitely a fire flower. After finding a white Vine, climb it and get a P-switch. Turn the frozen Munchers above a pipe into coins and go into it to get a Hammer Suit!
Fortress
Practice killing Thwomps, Boo Diddlies, and Stretches in this fortress if you have your Hammer Suit on. Rotodiscs and Spikes, however, must be avoided even if you're Hammer Mario. In the second room, there are just 3 Boo Diddlies that you can kill with Hammers, but otherwise you must simply avoid. The room will rise, and enter the door to get to Boom Boom's room.
Airship
This blue airship has enemies just like those in earlier airships. After entering the pipe, kill Lemmy Koopa 3 times. If you still have the Hammer Suit from 6-10, the king will say, "Hey you! Shall I borrow your clothes?? No dice! What a drag!" The Princess will give you a P-wing.