Yoshi's Eggs
When you find one egg, go to the toy box and you unlocked a code to find any of the eggs.To find the first egg go to 1-1. Then, go to the two pair of steps, jump in the middle and move to the left and jump and an egg should pop up.

Level Warp
At level 4-2, go to the right of the first falling platform (under the 3 boxes) and jump under each one of them to get the 3 hidden blocks. Use these blocks to hit the first blue block to get a beanstalk. Climb this beanstalk to warp to level 6, 7, or 8.

10 Lives
At the Menu screen, select the toy box and play the card game. Continue to play the game until you get a card with the princess on it. Now exit and start a game. You will start with 10 lives.

Switch Marios
To become a more powerful Mario, select Boo from the main menu screen.

Then when you're at the level select screen, keep pressing Select until you find the mario you want to be, such as: Super Mario or even fireball Mario!