Right here you'll notice pumpkin wearing Goombas, a clear reference to Super Mario World after you beat the game, where all of the Goombas started to wear masks. To kill one of these, just spin attack one then jump on its head. If you want to do it in a cooler way, then spin attack the pillar near the beginning to get a Rainbow Star, which will allow you to kill them all very quickly.
Go forward and you'll notice that a Chomp is coming your way. Head to either the left or right gap and wait until the Chomp passes you by. When it does, keep on going fourth. Afterwards, go inside of the mansion. There are Boos inside here, though you're not allowed to kill them like you were before in the same fashion. Instead of jumping on their head as you could in Super Mario 64, you'll have to direct them into the light.
The second Boo that arrives has a key inside of it. You see the switch near the entrance? Well, spin attack it so that a light will shine down. Direct the Boo(s) into the light to get the treasure. Once you run into the key, a door on the second level will open, so go through it.
In this area, you'll have to collect five star chips, though as you notice they're going all over the place on different levels. Get the first one on the far left side of the first platform; you may have to wait a second or so before it comes down, though when it does, just go in and get it. The rest of them just go around the stage, and from what I see there's no set pattern, so just go up the walls (via the ramps) and collect them all. Dodge the obstacles, most notably the windows which have a black hole, as if you fall down you'll die. Once you've found all five star chips, a launch star will appear in one of the windows that had a black hole near the beginning. Go through it.
You'll be launched on the outskirts of the mansion. You'll see Luigi in the window, who'll be calling for his brother to save him, though currently there's nothing you're able to do here. Head right and use the pull stars to get the key below. However, the second you get the key, quickly grab onto one of the pull stars before you fall into the spikes below.
Go into the now opened room and dodge the two Boos here. Grab the ? Coin, which will cause a Boo mushroom to appear. Grab it and you'll turn into Boo Mario. Boo Mario will be able to fly higher by repeatedly pressing A, and can vanish for a second by swinging the Wii remote. When he's invisible, he can go straight through particular bared walls. When you see the first set of bars, simply swing the Wii remote and go through it. Dodge the light and go through the final gate. Now go through the light to transform back into regular Mario and use the trampoline to shoot yourself to the other side of this ledge. Rescue Luigi and he'll get you a star!
Note: Completing this mission opens up Luigi's set of missions the can only be attempted by receiving a Luigi letter through the mailtoad.
Once again, you'll have to use the launch star at the bottom of the ship here. Continue on as you did before and dodge the Chomp. It's a bit harder to dodge it this time since the safe spots are now elevated upwards, meaning you'll have to jump to get there, though it's not problem. After it passes, go forward and use the pull stars to get to the other side. Once you do, go through the launch star.
On this planet, walk up to the "spooky speedster", or rather the Boo and he'll challenge you to a race. Accept his challenge and start off by using the pull stars to get across quickly. Eventually you'll come across... eh, some sort of meat. Try your best to get around it, as if you run into it you'll bounce backwards. Go through this by using the pull stars to continue on.
You'll end up soon enough to an area where a bone thing is rotating counterclockwise, you should also go this way using the pull stars just to be safe, as going the other direction can be a bad choice as the bones from the rotating thing will possibly block you. The last obstacle are a bunch of mines in the air, get past them and then land on the planet ahead. Quickly go up the star and the race will finish. The Boo will give you the star, which you will probably want to collect.
Go into the mansion and you'll notice there are a bit more Bowser statues than before. You'll also see a painting with a black Boo on it. It's actually a painting of a Bomb Boo, a new type of species that you can use as a weapon against your enemies or to use to break objects, such as those statues right there.
So, when one comes out, spin and Mario will grab the Boo's tongue and start to swing it around. If you don't swing the Wii remote, then Mario will barely swing it far, though if you do swing it, the tongue will stretch and the Boo will go farther. You get it? Well, anyway, break the Bowser statue that's blocking the fireplace and then go through the recently revealed launch star.
Kill the spiders and go onto the moving platform. Next, you can jump onto the Sling Pod, you remember, the ones from the Space Junk Galaxy? Anyway, sling upwards, dodge the Goomba and use the next Sling Pod to fling yourself into a sling star, which when used will shoot you into a launch star, which of course you should use.
In this area there are two more Bowser statues that you can destroy with the Bomb Boos to get a 1-Up. Next, you'll have to use the Sling Pods to get all five of the star chips here. Use the sling star as well to get one above. After you get them all, a set of pull stars will appear, use them to get to the launch star.
You'll land on some sort of object that has a rubber middle that you're allowed to bounce on. It's not hard to do, but it sure is fun! Find the launch star and use it to fly to the boss level.
Right away, feed the Luma if you want a Life Shroom or a 1-Up. I suggest the former, though that's just me. Head downwards, getting the star bits on the sides if you wish. When you get in the middle, the boss, Bouldergeist, will appear. Right now it's just a head. It attacks by thrusting rocks your way and raising rock spires out of the ground. Some of the rocks that its throws are gray, black and gold. If they're gray, then they're worthless. Black ones will turn into Bomb Boos, and gold ones will turn into gold coins in case you're harmed.
Anyway, when a Bomb Boo appears, use it and make it hit the boss. You're actually allowed to carry multiple Bomb Boos - as many as you can in fact, and as you could guess it'll deliver more damage to the boss. After you hit the boss three times with Bomb Boos, all of the rocks on the bosses' body will vanish and he'll just be a ghost looking creature. Now you must use the Bomb Boos he spawns and attack his core once. After this, he transforms back into his previous form, though he'll now have hands which certainly raises the difficulty.
Try your best and hit his head only. If you get rid of one of his hands (via the Bomb Boos), it'll be recreated within a set time limit, though that might give you a better shot at the primary target. In this form, he'll perform the same attacks as before, though will also use his hands to punch and to slam the ground. It's simple to avoid both of these attacks thankfully! Anyway, hit him three more times in the head, and he'll once again turn into his ghost form. Attack him once more with a Boo Bomb, and the boss will die. Collect the star and end the level!
And last and certainly least are the Boo Bombs. They're not too bad, though if you run into one, it'll cost you your life, so watch out! It took me about 10 tries, though I eventually bested here.
One of the worst things about the stage is the fact that the timer will continue even after you've found all purple coins. I died once because of this, so don't let this happen to you! The star will appear in the middle of the stage, so try and reserve your final coins in that general area.
Now, right away you'll probably notice the platform to the right. Go onto it and it'll start moving right. While the platform is moving, be sure to dodge the Boo and continue on. Get the key that is stationed on another platform to open to door ahead, then go through it.
Now, jump onto the platform to the left and grab the ? coin. It'll cause the platform to move left. After this, the spotlight will shine on some platforms ahead, so go north and up the stairs. Ignore the ? box and then go right, jumping over the gaps and dodging the Boo. Eventually you'll have to go south, so do so. The platform will be quite narrow now, so go slowly if possible.
Keep doing down until you see a flight of stairs to the right, go down them and continue to dodge the Boos. Now go up into the large room here with a key in the air. Grab the key which will cause two closets to open, with star bits in the right one and a ? coin in the left. Get the ? coin, which will cause the spotlight to go up. Jump on the platform and then on the bookcase, then backflip onto the ledge.
Grab the key and continue upwards. Grab the key to the left of the stage here and grab the 1-up that comes out if you wish. Continue backflipping or wall jumping upwards and get the key at the top, which will cause the door to open, thus revealing a star.