The Secret Undersea Cavern

Smash the Rock Wall: First things first, jump into the water. You'll see a bunch of green shells scattered around the ocean floor. Grab one – you'll need it. There are also some chests floating around if you want to grab some Star Bits or maybe even a 1-Up Mushroom. Once you've got your shell, head towards the cracked wall that's right behind the penguin. Chuck that green shell right at the cracked wall. Boom! It'll break open, revealing the entrance to our secret cavern.

Secret Cavern: Now you're inside the secret cavern. It's pretty full of wooden crates, so smash 'em up! You'll find more Star Bits and even a Goomba in there. Keep going to the end of the cavern. You'll see a big fence. Look around for some more crates you can break open – one of them will reveal a hole you can slip through. Inside, you'll find a tree stump. Do a Ground Pound on it (press ZL/ZR + A/B while in the air) and voilà! The Star Launcher will appear.

Tox Boxes and Thwomps: This next part can be a bit of a pain, so pay attention. You'll encounter a new enemy called a Tox Box. Think of it like a Thwomp, but it rolls around on a path. If you're in its way, it'll flatten you instantly. The trick here is to watch its path. When it stops and opens its mouth, quickly stand on the tile it's about to land on. This will protect you, and you can then sneak behind it.

Navigating the Platforms: After the first Tox Box and Thwomp, you'll reach a section with several rotating platforms suspended over a waterjet. Seriously, do NOT fall into that waterjet. It'll suck you into a black hole and send you right back to the beginning of this section, meaning you have to deal with those annoying Tox Boxes and Thwomps all over again! The best way to get across is to walk up with the rotating platform, then jump to the next solid platforms. Keep an eye out for concrete blocks that'll try to knock you off.

The Stone Path: Once you've successfully navigated the platforms, you'll come to a stone bridge that leads you up a stone path. This path is also guarded by more Thwomps and Tox Boxes. Just remember the strategy: don't be on their tiles when they smash down! There are a few 1-Up Mushrooms scattered along this path. If you're struggling with the Tox Boxes, try to grab these 1-Ups to give yourself a buffer in case of a game over.