Tiny Pyramid
Go to Shifting Sand Land and stand on all the pillars. Make your way to the top of the pyramid and jump into the hole. As soon as you get into the elevator, press the X button to look around. As the elevator goes down, the level should get smaller and smaller. Ghost Rabbit
As Wario, arrive at the Boo-infested courtyard and position yourself so that a Boo is between you and the rabbit. Dive for the rabbit, and the Boo will knock you away while you catch the rabbit. Now, if you walk back to the rabbit, it will not move and become untouchable. Infinite coins
At Cool, Cool Mountain, proceed down to the cottage and go down the slide. Exit the cottage and kill the three Goomba's and grab their coins. Now, use the warp and repeat the above steps and the coin counter will reach 255. Infinite stars in multiplayer mode
In multiplayer mode, obtain the Wario hat and grab a player by standing next to them. Now, try and punch them, then throw them and grab the star that falls out of them if they have a star. Pick up the enemy again, and ground pound them with them in your hands. They will drop another star, even if they have none in their count. Repeat for as long as you like. Walk like normal underwater
Enter Wet-Dry world, and set the water level so just the tip of the large gray spiral ramp is in the water. Now, swim around to the underside of the ramp, and swim up towards the ramp while jumping. If done correctly, you should fall down to the bottom of the level, and be able to move like normal under water. Walk Underwater in Dire Dire Docks
When Bowser's Submarine is still in the docking area, head to one of the rear propellers. It is just slightly above the water. Now, while underwater, jump up under it then quickly Ground Pound. Your character will fall through the water and land at the bottom. You can now walk underwater, so you can easily grab several of the Stars that lie there.