Super Mario Bros. · NES walkthrough

World 2

First underwater course, leaping Cheep-Cheeps, and Podoboos in the castle. Four stages. Previous and next stage links sit under each area.

World 2-1

Overworld Timer 400

Reach the flagpole. Optional vine to a coin sky, optional coin pipe.

Overworld again, with more pipes and Troopas.
A beanstalk block on a ?-block platform leads to a coin sky (optional). You return later in the course.
A pipe in this stretch leads to a coin room (optional).
Near the end, a springboard can clear a high wall. A hidden coin block also lets you step over that wall without the spring.
Flagpole.

A hidden 1-Up in this course is documented as appearing only if you collected every coin in World 1-3 or warped into World 2-1.

Underwater Timer 400

Swim to the exit pipe. First underwater course.

The start pipe drops you underwater. Swimming uses jump to stroke.
Bloopers do not reach the very bottom. Small Mario can stay low.
Holes in the floor are drains. They pull you down — swim out hard if you dip in for coins.
The exit pipe returns you to a short overworld run to the flagpole.

Bridges over water Timer 300

Cross short bridges while Cheep-Cheeps leap from below.

Cheep-Cheeps jump from under the bridges. Fire Flower helps; otherwise time jumps so you are not knocked off.
Treat short bridge sections one at a time until the rhythm is comfortable.
Flagpole. Collecting every coin here is a documented condition for a later hidden 1-Up in World 3-1.

Castle Timer 300

Reach the axe. First Podoboo castle.

Podoboos jump from lava. Time crossings.
Lifts under a low ceiling: jump from the edge or you bonk and fall.
Impostor on the bridge again. Axe still clears the castle. A lift over the fight is riskier here because of ceiling blocks.