A guide to completing World 6-1 in Super Mario Bros 1 for the Nintendo Entertainment System.
Explore World 6-1
Go to the right to find two ?-mark blocks that just contain coins. To the right, a Lakitu will begin dropping Spiny Eggs. Beware of the Spinies as you go up the stairs on the right. If you hit the leftmost brick at the top of the stairs, you get a Mushroom or Fire Flower. You can also try to jump onto the bricks to stomp the Lakitu or hit it with a fireball.
After the stairs, there are some bricks. Hit the rightmost brick to get some coins.
Go to the right, jump a gap, and get the three coins there. Then go up the stairs, get the two coins after the stairs, then jump up another set of stairs, but beware of the Lakitu that appears. If you want to stomp it or hit it with a fireball, make sure not to go too far to the right. Just after the bricks at the top of the stairs, fall straight down onto the lower set of bricks, then go to the left. If you collected all the coins in World 5-3 without dying, or if you warped to 6-1 via Warp Zone, you can go to the left until you're up against the blocks, then jump straight up to find a hidden 1UP mushroom.
From there, if you didn't stomp or burn the Lakitu already, you can try to get on the bricks to do so. Or just ignore it and avoid the Spiny Eggs and Spinies that it drops.
Go to the right and get past the Piranha Plant pipe, get the three coins after it, then before you go past the bushes, stand in the middle of the darker, rounded bush that has big dots on it, then jump straight up to find a hidden block that contains a coin. Jump on top of that block and jump straight up to reveal another hidden coin block.
Go to the right to find another short staircase, where another Lakitu will appear. If you hit the leftmost ?-mark block, you get a Mushroom or Flower.
To the right, after another short staircase, there are three brick platforms. The rightmost brick of the middle platform contains coins, but if you're tall, you will have to run and crouch to slide under and get the coins. You can safely stand up afterward because you'll move right, not left into the pit.
Another Lakitu will appear as you go to the right. Go right, then up the tall stairs, jumping over the gap on the way. At the top, make a running jump to the right to hit the goal pole and go to World 6-2.