A guide to completing World 5-1 in Super Mario Bros 1 for the Nintendo Entertainment System.
How to Clear World 5-1
There are nine monsters to the right, starting with a Koopa Troopa. You can stomp the Troopa and kick its shell through the remaining enemies, but be careful not to let the shell hit you when it bounces off of the pipe on the right.
When the Piranha Plant is not in the way, jump on the pipe, then jump over the gap, and get past the second Piranha Plant pipe.
Up ahead, there are eight enemies, starting with a Paratroopa. You can stomp the Paratroopa twice, then kick its shell through the remaining enemies, but the last enemy is a Paratroopa that might bounce over the shell.
When you get past the enemies, jump onto the blocks, then jump and hit the middle brick to get a Starman. As you go to the right, you'll go past a cannon that can shoot Bullet Bills, but if you're running past it, it might not have time to shoot.
After you get past a large group of enemies, you find a pillar of blocks, and some bricks with a gap between the blocks and bricks. If you collected all the coins in World 4-3 without dying, or if you warped to 5-1 via Warp Zone, you can go down below that gap, then jump up to get a 1UP Mushroom from the hidden block.
To the right, past a pit, there is a cannon with a Piranha Plant pipe above it. Go down into that pipe to enter a secret area. Jump onto the brick on the right (which contains coins), then jump on the platform to the left, then jump left onto the ceiling, where you can try to jump left then fall right to enter the area with the coins.
After you exit the secret area, you'll be on the pipe to the right of the cannon you saw a moment ago. There is also a cannon to the right of that. Beware of the Bullet Bills and jump over the cannon on the right. There are two Paratroopas after the cannon. When you get past them, go up the stairs, jumping over the gap to reach the top. Make a running jump from there to hit the goal pole and continue to World 5-2.