When you first start the game don't get out of bed on the first level. You'll get kicked out of the castle and the alternate story begins. This is the shortest way to beat one of the endings. After you beat an ending you can go back and redo any level to find the treasure and/or map piece.
To access a hidden chapter, start a new game and let the pirates knock the sleeping Mario out of the castle.
If you have trouble roll jumping in a Wood scene, remember that sometimes the grass belows helps. When you roll, you'll be in long grass. Once the long grass ends, it indicates when you should jump [press A] to get into a certain spot that needs Roll.
To stop conveyor belts having any effect on you, carry a stunned enemy when you need to walk on one. you'll be able to move around as if you were standing on a platform.
Successfully complete the game with a 100% status with all treasure and map pieces. Then the levels on the map that have a Boss at the end will have a skull nearby, marked with an arrow. Choose one of these levels. Then at the level name screen, hold Down and press A. The game will proceed directly to the Boss.
Flagman D.D. mini-game:
Successfully complete the game with a 100% status with all treasure and map pieces. Then a bonus game can be played after the final level.