A guide to completing World 5-4 in Super Mario Bros 1 for the Nintendo Entertainment System.
Explore World 5-4
To the right, there is a large fire pit, with Podoboos jumping up and down, and a big scary fire bar spinning around in the middle. You can try to jump on the middle platform to hit the ?-mark block and get the Mushroom or Fire Flower from it, but you will have to avoid the giant fire bar.
To the right of that, there are two possible paths. The path on the bottom is easier to go into, but it has more fire bars than the upper path. Whichever path you choose, you will probably have to stop and wait, or crouch, or jump, to avoid some of the fire bars.
After that, there is a fire bar just before two sets of moving platforms, one going up, one going down. Beware of Bowser's fire breath, and the fire bar on the other side.
To the right of that, there is a fire bar with some coins below and above it. The coins under it will be difficult to get if you're tall, but you can try to run and crouch to slide under and get them.
To the right, there are two flame pits with Podoboos going up and down.
After that, you will reach Bowser's suspension bridge. There is a Podoboo jumping up and down near the left side of the bridge. There are bricks above the bridge on the left, but there is a moving platform above Bowser's head that you can try to jump on to get past him. As usual, if you're Fire Mario, you can hit Bowser with fireballs to defeat him (and to discover ). Otherwise, try to jump over or run under Bowser.
Afterward, you'll meet another mushroom retainer who says their princess is in another castle. Then you'll continue to World 6-1.