Note: Not all of these are verified, so use at your own risk and/or waste of time!

As many mushrooms as you want

When at the kitchen, you can go up the steps.(to the left) instead, go to the right until you reach a mushroom. get the mushroom and then go inside of the kitchen.then go back out and the mushroom will be there again. repeat for as long as you want because the mushroom will never go away.

Secret star in freeze flame

Go up the mountain to the sling star,then be fire Bario to kill snowmen,until you reach the top. Its called conquering the summit, and you can jump down to baron brrs area from the top.

Dreadnought’s Ammo Depot

In the last mission of Dreadnought, go underneath from where you land. Jump in the pipe, and you reach the Ammo Depot. It is similar to Battlerock, but there is more trash to blow up with the Bom-Boms. It is very hard. Good luck!!

Beating Bowser for the last time

If you want to beat Bowser when you meet him at the top you’ll vs him there’s 3 stages. Stage 1 beat him like how you beat him. Stage 2 one he will go all spikey then hit him with those things. Stage 3 he’ll turn in to a rock type thing spin in to him then repeat this about 4 times that is how you beat Bowser for the last time.

Spin swim

To swim faster you need to swim BUT if you are underwater it will drain your air so it is only good if you are racing on top or near the top of the water.

Trial Galaxies

Trial Galaxies are harder versions of Ray Surfing, Bubble Travel and Ball Rolling. To open the Trial Planet you need to find three green stars located in Bouy Base, the desert galaxy.

Dino Pirhana

To defeat the dino pirhana you have to spin attack his tail to break him out of his shell then hit him three more times to kill him. If you feel you out run him keep hitting him with star bits while you are running and it slows him down.

Super Mario Super Size!

When loading up the game press and hold the “2″ button when the loading screen appears – this will make Mario 3 times as large until the first time you die.

Grand Finale Galaxy

Collect all 120 Stars with Luigi, and defeat Bowser to unlock the Grand Finale Galaxy, which is the Star Festival seen in the beginning of the game.

Star 121

Collect 100 Purple Coins in the Grand Finale Galaxy to get the final Star.

Pokemon reference in Buoy Base Galaxy

In Buoy Base Galaxy, above the tower where you collect the Blue Star Pieces, is a little planetoid that is a sphere with two red panels on top and a lighter bottom with a screw in the middle. It looks exactly like a Pokeball.

Green star in Byou Base

Go to Byou Base and then go down in the water you will see a pipe (the one in mario the green one) then lead a torpedo and smash the big thing covering it then enter the whole then you will see stuff to let you walk on it and missiles will go after you then smash the thing around it again then get the green star.

Pikmin Easter Egg

In Space Junk Galaxy, the space ship planetoid is Captain Olimar’s ship from Pikmin.

Garbage Dump

In Battlerock there is a secret. When you are on the lop-sided planet with all the rolling balls find the hungry Luma. Feed him and he’ll transform into a launch star. Launch out of it and talk to garbage man! You’ll get an extra star.

Level skip on deep dark galaxy

On the deep dark galaxy (first mission) get in the cannon and point it far to the left then fire it above the handle bar (if you miss you’ll go flying past) if you do it properly you will fall down right after the bar.

Beach Bowl’s Secret Star

To get the secret star, get the gold shell, go to the right side of the planetoid, hit the treasure chest, then go in the launch star. You then use Ice Mario to wall jump some waterfalls to reach the power star.

Goomba slap

If a hole in the floor leading to a black hole is near you and an goomba is close to the black hole go to the goomba before it chargers to you shake the wii remote and it will spin into the black hole and turn into starbits.

One foot toad

Go to sleeping toad and zoom the camera in. He will be smiling and if you look at his feet, he will only have one foot.

Trial Galaxy’s Gravity defiance

After unlocking grand finale galaxies, it is possible to exit the gravity of the trial planet by doing a homing attack on the luma that leads to the galaxy. If you do it right you should exit the planets gravity. You should be able to get there with flying mario, but you will be unable to fly on the trial planet.

Watermelon

Collect 9,999 star bits and get back to observatory by getting the star. All coconuts are now watermelons!

How to get lot’s of starbits

It’s really simple. First, go to Sling Pod Galaxy. Collect all the star bits and throw one at one of the lumas. Then go back to sling pod galaxy, collect all the starbits and repeat the glitch again. This is a really fast was to get 9999 star bits to transform your coconuts into watermelons!

Purple Coins

When you are either swimming or flying mario (not to be confused with bee mario), if you spin near purple coins, you will absorb some purple coins around you.

The following are from IGN
Unlockable: 121st Star

There’s actually 121 Stars in the game, not 120. To get it, you must first have all 120 Stars. This unlocks Luigi. Beat the entire game with Luigi, defeating Bowser at the end. After this, a new galaxy will be unlocked. Finish this final galaxy to get the 121st Star.

Unlockable: Luigi

Here’s how to get Luigi. First, get all 120 Stars in the game. Then, return to Rosalina (on the Comet Observatory) and request to fight Bowser one last time. Defeat him and let the credits roll. Thereafter, a message will appear telling you Luigi is a playable character.

Unlockable: Death Count

The Grand Finale Galaxy, which is the secret galaxy that can be unlocked after 120 Stars are gathered with both Mario and Luigi, holds another secret. Once the final Star is acquired with both characters in this galaxy, you will be able to see your death count on your save file. This will allow you to see how many times you died while playing the game with both Mario and Luigi.

Unlockable: Additional Demo Stages

If you’re playing a demo version of the game at a kiosk, try holding down the 1 and 2 buttons as you press A and B to start the game. This will unlock additional stages for you to play through.

Hint: Second Player

If you have a second Wii controller, you can have a friend play along with you. While there won’t be a second player on-screen, you will have a second cursor to use. This means that Coins, Star Bits, and the like can be collected by the second player. There’s also some functionality in controlling Mario’s jumps.

Hint: Extra Lives

Because you start each game with only four lives (after shutting the game off and turning it back on), you might be in need of some extra lives upon rebooting the game. You can usually get five right off the bat from Toad (he’ll run around with a letter above his head, symbolizing a letter from either Luigi, or more likely Peach). There are four more strewn around the Observatory that you can acquire, however:

* 1.) On the moving green platform below the core.
* 2.) Under the stairs leading to the kitchen.
* 3.) Right at the top of the observatory. (Once the Red Star is unlocked)
* 4.) Underneath the entrance to the gateway to the stars. (Once the Red Star is unlocked)
* 5.) Next to the StarShroom (in a crate)

Hint: Enemy Sacrifice

This may be an obvious hint, but it’s one worth stating nonetheless. When you fight most enemies, you can control what comes from their dead bodies when defeated (a sort of “sacrifice”). By jumping on an enemy, which is usually the more difficult way to kill most foes, a Coin will appear. Spin-killing or using other methods will usually result in a few Star Bits.

Hint: Infinite 1-Ups

If you grab any 1-Up Mushroom at the Comet Observatory, you can then head into any dome, back out, and arrive back at the Comet Observatory without having played any stage. This will make the 1-Up Mushroom you acquired reappear.

Hint: Super Stomp

If you want to do a specialized stomp with Mario or Luigi, try the following. When you jump, before you press the Z button to do the Ground Pound, spin by shaking the Wii controller. As you are spinning, you can then press the Z button. The result? A stronger stomp that will actually track the enemy and follow it, kind of like a heat-seeking missile!

Hint: Green Star Locations

Battlerock Galaxy: After rescuing Luigi from the haunted mansion, he’ll start helping you find power stars. The second star he finds is on Battlerock. Go rescue him and get the star.

Buoy Base Galaxy: As soon as you get there, dive underwater and get the underwater missiles to hit the cage blocking the green pipe. Head down there, and you’ll pop up on the bottom side of the plane. There will be missile launchers everywhere, so make sure you have full health and good jumping skills. The star will be inside. Get a missile to hit it and you get your second green star.

Dusty Dune Galaxy: On the second level of Dusty Dune, where you start, right underneath is a Hungry Luma. Feed him the amount of star bits he wants, a new planet will form and a launch star will shoot you there. Now, you must collect all 5 silver stars. This part is like an elevator thing; you land on the button and you go up or down go in every direction you can until you have all 5 silver stars.

If you made it this far, here’s a link to a walk-through: Click here (opens new window)