Before you dive into the pipe leading into the cave proper, you encounter a Koopa Troopa. Stomp on it to boot the Koopa from its Shell, another stomp on the Koopa will finish it off. You can get acquainted with your capabilities with a Koopa Shell in this small space.
You can pick up a Fire Flower from one of the ? Blocks shortly after arriving in the cave. If you arrived in the cave with the Cat Power-Up, try to keep it on standby in your item storage. Try to stay Mega, you can ground pound through the two bricks on the ground to reach a small side area.
Watch the Ricochet!
It’s easy to hurt yourself in this cave now that Koopa Shells are a factor to consider. There are plenty of small locations in the caves where you can get into trouble if you carelessly kick around a Shell and then forget to watch where it goes.
A lone Koopa Troopa guards the area below the Fire Flower. You can use its Shell to break open the Crystal Blocks and ? Blocks here.
Green Star #1
The first Green Star is easy to collect; it’s found right after you take the Clear Pipe out of the first cave section, hovering between two columns of moving cloud platforms.
From the two floating cloud columns, you have a choice. One is to take the main, obvious path that leads directly to the Checkpoint Flag. This leads you to a Mystery Box that takes you to a side chamber where Green Star #2 awaits.
However, you can use the rising and falling cloud platforms to reach an upper route that takes you over the Checkpoint Flag. If you keep following the upper path, you’ll encounter a pipe that takes you to a golden chamber containing three gold Koopa Shells. Kicking these around the room will earn you a hefty sum of Coins.
Green Star #2
The Mystery Box on the lower level takes you to a bonus room where you must defeat two Koopa Troopas in 10 game seconds. Doing this earns you the second Green Star.
Stamp
After the second winding Clear Pipe leading out of the second cave section, use the ground pound to reveal the location of invisible ? Blocks. Use them as steps to reach a ledge patrolled by a Koopa Troopa.

The wall there also contains another Clear Pipe you can dive into; it leads to a hidden chamber where you can find the Stamp for this level, next to 7 stacks of Coins.
Green Star #3
The final Green Star is found close to the Stamp, wedged in the middle of a Goomba Tower. A single ground pound at the top of the tower will wipe them all out, but it can be hard to successfully aim. Fireballs or a Koopa Shell also work great. Afterwards, you can move on to the Clear Pipe that will take you to the Goal Pole area.
Completing 1-2 unlocks 1-A and grants access to a Toad House on the World Map.
On Toad Houses...
Toad Houses can appear on a World Map after you have beaten certain levels, or they can be found hidden in side routes on the map. These Toad Houses have two Gift Boxes inside them: a small one and a large one. You can hit only one of these boxes for a reward; the other will disappear. The contents are also randomized, so there’s luck involved in trying to get some good items.
After you visit a Toad House, it will disappear from the map, and will only return if you continue after running out of lives.
Tip
This level contains a hidden Warp Pipe, accessible only with the Cat Power-Up, that skips past the rest of World 1 and starts you on World 2.