To play the bonus games at any time, hold Select and press X, X, Y, B, A on the map screen. A menu will appear with all of the mini battles, two of which can be played against another person.
In the level select screen hold the select button and press: X, X, Y, B, A.
At the end of every world there are two question mark boxes. When you get a 100 on every level on that world those two levels will appear.
In Sluggy the Unshaven''s Fort, go in the door at your left at the start. Next, use a POW or ? bubble item. A door will appear. Go through it to recieve a secret code.
On level 1-3, If you go to the second advice box jump high to the left. If done right you will come upon a ledge. Run to the left and recieve 95+ coins.
Find the secret Beanstalk
When you are on level 1 7 at the end after you have gone through the tunnel, there is a log. Go to the top tip of the log and jump. Then a bouncey ball will come out. Jump on that and you will go up. Then go to the left and roll the rock. A question mark will appear hit that and you will go up a beanstalk.
Level 3-8: Pirahna Quick Kill (Cheat)
After sliding down the tunnels and landing in the water, swim right in the water and jump up to the far left edge of the white platform. Before Kamek appears, shoot the small Pirahna Plant to win the boss battle easily.