To beat the first galaxy boss (Jr bowser robot), you must crawl up Megaleg's ramp (in between the two feet). Then, you will eventually reach the head, where the grand star is under a glass dome. There should be two bullet bills firing somewhere, and if you let them see you, they follow you, and if you jump over the gate blocking the dome the bullet bill will follow you and smash the glass dome, freeing the grand star. Presto!
Beating the bear in "the dirty tricks of Major burrows"
In order to beat the bear, you must let it come from the ground and you ground pound immediately. Then you spin and hit it. Repeat this until it gets really mad. Once it comes out of the ground and you ground pound, it goes back into the ground and then it starts to wave its hands and get you. As it does that, you have to ground pound and spin to finish the level. Good luck!
Bonus Levels (Demo version)
Instead of just pressing A + B at the main menu of the demo, press and hold 1 + 2 when pressing A + B to access two additional stages.
Buoy Base Galaxy: Pokemon reference
In Buoy Base Galaxy, above the tower where you collected 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.
Coconuts become watermelons
Collect 9999 star bits in the hub, and all the coconuts in the game become watermelons.
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.
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.
Extra 1-up in Comet Observetory
If you go to the garage (the place where the lumas build the starship) next to the starship there is a create. Smash the crate and you will have a 1-up in there.
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.
4. Underneath the entrance to the gateway to the stars.
Fart Noise
If you go to the Comet Observetory, go to Roselina. If you talk to the luma right next to her, it will kind of make a sqeaky fart noise!
Flying mario
To use flying mario in the comet observatory, you must beat the level Gateway's Purple Coins.
Freeze enemies
You must have 2 wii remotes to do this. As player1 plays player2 uses the cursor to freeze the enemy note: player2 must hold the a button on the enemy or it will unfreeze. Note2: this does not work on any boss. Note3: if you can't see the enemy on the screen any more after moving away it will unfreeze.
Grand Finale Galaxy and Star 121
To unlock the final star and galaxy, collect all 120 stars with Luigi and beat Bowser. Doing so unlocks the Grand Finale Galaxy, which is the Star Festival seen in the beginning of the game. Collecting the 100 purple coins in this galaxy gets you the final star.
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 ammount 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.
Hidden Character
Get all 120 stars. Return to Rosalina on the Comet Observatory and request to fight Bowser again. Finish the credits and you will get a message saying that Luigi is now playable.
Homing Attack
Spin in midair, and then immediately press Z to do a homing attack on the nearest enemy or breakable item.
How to get a hidden star
Go to the beach bowl galaxie in the second mission and get the gold shell. Then go near the giant waterfall to find a chest. Break it with the shell and you will see a launch star. use it to get to a secret area. Then There will be an ice flower grab it and you can wall jump in waterfalls after some practice you can reach another area. I wont say where but there is a star there!
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.
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.
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.
Star 121
Collecting all 100 purple coins in the Grand Finale Galaxy.
Starting Boost When Racing Cosmic Mario
When the countdown timer starts as you are racing Cosmic Mario, hold forward, then as it hits 2, hold down on Z to crouch, and when the race starts hit A right away and you will turn yellow for a few seconds and get a really good boost that will put you way ahead of Cosmic Mario.
Super Groung Pound
At the top of a normal jump, spin and groung pound at the same time. If succesfull, Mario will spin in the ground pound and flip.
Super jump
When you are playing hold down the Z button, then press A and then you will have a super jump.
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!
Unlock Flying Mario
To unlock Flying Mario, you must, sadly, have access to all the domes. Once you have done this, go to the Gate dome. To get there, go up, past the engine room, use the teleporter and you can go through the gate. You'll find yourself in the place where you caught the Luma rabbits at the beginning of the game. Go to the castle and speak with a red Luma. He'll tell you to collect 100 coins. Then you can use the flying star to do so, and collect the ones on the ground. Once you have done this, return to the observatory and look around on top of the bedroom, or near the terrace for a red star. Use it, and you can fly around for a while. (They respawn once you've used them).
Watermelon Mania
Collect 9,999 Star Bits (the maximum amount) to convert all of the game's green coconuts into watermelons. This cannot be reversed -- hope you like watermelon!
Zelda Rupee
Once you have unlocked the Rolling Gizmo Galaxy as one of the trial galaxies go into it's level. Walk past the ball and get on top of the metal cubes. Do some fancy wall jumping onto the bridge. Once on top, go to the edge and pan the camera down. You will see a Zelda Rupee made out of star bits.