Getting to Soda Lake
Soda Lake is a secret area within Mario World that you can only access by performing a slightly difficult maneuver in the Cheese Bridge level. When playing the Cheese Bridge level, make sure you have caped Mario (the Mario that can fly) and Yoshi. When you reach the end of the level, you will see the usual exit with the pole that oscillates up and down. Instead of going through the exit, fly underneath the exit with Yoshi. After you fly past the exit, jump off Yoshi and onto the platform the exit is on. This will place you behind the exit. Continue walking forward and grab the key in front of you. Simply walk towards the black key hold in front of you while holding the key and you will unlock the Soda Lake.
Warping to Bowser's Castle
The quickest way to reach Bowser is by going to Star Road. One of the easiest ways to get to Star Road is by completing all the levels in Soda Lake. Star Road has five levels in it, each on on the point of this star-shaped world. Complete the levels until you reach the lower right level. Once you complete it, you will be given a warp directly to Bowser's Castle, enabling you to bypass the rest of the game.
Getting a Perfect on the Tic-Tac-Toe Bonus Game
At the end of almost every level there is an exit with an oscillating pole. If you hit the pole while exiting the level, you will receive a certain amount of points. The higher the pole is when you hit it, the more points you receive. Once you attain 100 points you get a chance to earn lives by playing a game of tic-tac-toe. You will automatically enter a room with nine boxes arranged in a 3 x 3 square. The middle square will have an image in it (either a mushroom, star, feather or fire flower.) The other eight squares will rotate around the middle square all while quickly flashing one of the four possible images. Your job is to get as many lines of matching boxes as possible. The easiest way of doing this is by pausing the game on and off until you see where the boxes will show the image you want. Once you learn the exact spot, step into that spot and hit the box. Repeat this method for all eight boxes and you should get the maximum amount of lives.
Bonus Level in Donut Plains
One of the most useful secrets is uncovering the bonus level in Donut Plains (this is the second world of the game.) Enter the first ghost house in Donut Plains with caped Mario. When you enter the ghost house, run and fly to the left of the screen. When you reach the highest point of flight you will enter a small opening in a platform. Move to the right to land on the platform. Continue walking to the right until you reach the end of the platform and then drop off. You will see four yellow blocks and a door. Simply enter the door and exit the level. This will uncover a secret bonus level. This bonus level has three question mark boxes in it. The middle one has a Yoshi egg and the other boxes have either a feather power-up for caped Mario or a flower for fire Mario. Enter this level any time you need Yoshi or a power up.
Easy Extra Lives in Donut Plains
Once you unlock the bonus level in Donut Plains by beating the first ghost house the secret way, you will have access to a Yoshi egg and two power ups (a feather and a flower.) If you enter the bonus level with a Yoshi already in hand, the Yoshi egg will bear a 1-up mushroom. You can enter this level and get this 1-up as many times as you want.