Super Mario Bros. 3/World 8

This is the final world of Super Mario Bros. 3! It is all dark.

Tanks
Kill or avoid all enemies, this level is built just like the airships, except that it'll end with a Boomerang Brother and give you a starman.

Battleships
They rise and fall. At the end, enter the pipe and it'll take you to Boom Boom's room, and you just stomp on him 3 times.

(Variant: In Super Mario All-Stars, the corner removed from the last battleship returns, meaning that if you swim under it, getting back up is possible only with a Frog Suit, a P-wing, or if you time your jump when the ship is at its lowest point.)

Hand Attacks
In the first of these, it reviews all the kinds of Koopa Brothers, first a Fire Brother, then 2 Hammer Brothers, then a Boomerang Brother, and finally a Sledge Brother. At the end is a pipe that leads to a Raccoon Leaf.

The second practices your skills with avoiding Podoboos when leaping over pits.

The third deals with flying Cheep-Cheeps.

Airships
A P-wing is definitely good for this level. It scrolls by quickly! At the end is a pipe simply taking you to Boom Boom's room.

8-1
If you have a P-wing, you can enter a pipe and get into a room containing 3 1-Ups. Just avoid the enemies and get to the end of the level.

8-2
Just either enter or leap over the quicksand. If you leap over the quicksand, the Sun from the middle of World 2 will reappear. If you enter the quicksand, you just enter one of the pipes and it'll take you to a coin room. After exiting the coin room, just follow to the end, trying to avoid entering the bottomless pits. If you don't have exactly 2 star cards at this moment, I'm sorry to say it's too late to get a 5-Up. This is your last chance to get one if you do.

Fortress
There are 2 rooms, one is blue and the other gray. Most of the doors can be entered from either room. If you're Hammer Mario, kill the enemies that you see, otherwise you'll have to avoid them. Near the end of the gray room is a P-switch that will open a door on the far right and take you to Boom Boom's room. Duck to get past the spikes and you'll get there.

(Variant: In Super Mario All-Stars, both sides are blue, making it more difficult to tell which side is which.)

Super Tank
Last tank in this world. Just follow the screen, avoiding or killing enemies, and enter the pipe to get to Boom Boom.

Koopa Castle
This is it! The final level! Take the high path whenever you have a choice, and stay away from any statues of Bowser you find, as they can shoot laser beams diagonally. When you reach Bowser, he cannot be killed the way his kids and Boom Boom are killed. You must stand in one spot on the bridge as he jumps, avoiding the fireballs he spits at you, and get out of the way just before he lands. His impact will smash a hole partway through the bridge; three hits in one place will drop him off the screen. The door will flash, and now you get to meet Princess Toadstool. After that, you just watch the credits, showing you pictures of things that happen in all 8 worlds. Then you can re-do the game with 28 P-wings!