Super Mario Land 2: 6 Golden Coins/Turtle Zone

Located inside a giant turtle, the Turtle Zone is where the final coin holder, Pako the octopus, lies. You'll need to swim through lots of water before you can reach him. Pako resides in the whale's belly, and to get to him you'll need to navigate across some islands, traverse a sunken submarine and even enter the body of a whale. There will be a lot of swimming ahead, so be sure to pack a fire flower to defend yourself!

The islands
This level gives you a preview of what to expect throught this zone: lots of swimming. There are also a lot of new aquatic enemies that can only be dispatched by fireballs. Other than the Cheep Cheeps and the Blurps, there are also Harisenbon, pufferfish that attempt to block your path by puffing into a spiked ball and floating up, as well as the Jo, sharks that like to charge at you when you get near and are immune to fireballs.

If you can, try to stay near the surface, as you can leap out on to platforms for coins. There are some platforms you can't reach without a carrot, which is inconvenient, since you're in a water level. At the narrow columns near the end of the level, There is one that is low enough that you can leap to from the water. Jump from that platform to the one on the left and jump directly up to reveal a hidden block containing a money bag. The way to reach the bell is obvious, just jump out of the water when you're underneath it.

A sunken submarine
In this mazelike submarine, it is easy to get confused about where you should go. The bullet bills and Unera return to make your life harder, and you'll also have to deal with the fireball-immune Honebon and Jo. As if that weren't enough, there are also deadly ceiling spikes throught the sub that will lower when you swim near, as well as sea urchins. You will need good reflexes and good underwater control to make it to the end uninjured.

One block in a section above the water contains a Star, conveniently just before a staircase with exactly five koopas to give you an easy extra life. However, you'll have to enter the confusing block maze after that section. The path will split after going through the first pipe. From there, you want to take the two left pipes first as they're connected in a loop and will let you access a fire flower for small Mario and a 1-Up. Ultimatly, you need to take the right pipe that will lead to a room with a visible block containing a money bag. It only takes a few more steps to reach the exit to the maze. To reach the ending bell, you must use the two rising platforms, but be sure to jump off before they send you into the spikes.

There is an alternative exit in this level that is quite well-hidden. Read below to know about its location.

Tropical paradise
Curious and dexterous adventurers can stumble upon a hidden exit that lets them exit a secret hole in the submarine, leading to a special island. There a tons of coins in this level spelling out "Mario Land 2", though the first letter is initially a W. The obstacles along the way are simple enough to get pass, and you even get to choose between a fire flower and a carrot near the end. Completing the level will wake up the whale, which will start blinking as it tries to fall asleep again.

Into the whale
This level takes place entirely inside the whale, which, while gross enough by itself, also hides deadly threats. There are huge spikes and stalagmites putting out of the floors and ceilings, and some can even lower themselves to stab you! The sap you encountered back in Tree Zone makes a return, in the form of suspended goo that lets you wade inside or jump out of it. There's also a unique type of goomba called the Goomdiver, which behaves like a normal goomba but can swim around in the water. The level is straightforward, though you can find a money bag if you reveal a hidden block in a coinless gap at the suspended water section.

Boss: Pako
Being the last coin holder, Pako isn't going to give his golden coin up without putting up a fight. You need to fight him underwater, and he can send out invincible smaller versions of himself called Poko that home in on you. You'll need to jump on his head 3 times to defeat him, but the Poko can make this task more difficult that it sounds. You can also turn him into fried calamari by toasting him with 6 fireballs.

With all the coins retrieved and put into place, the door to the castle slowly opens. It is time for the final confrontation with Wario. Do you dare to venture into Wario's Castle?