To get lives up to 99 go to the first level in the game. From there, go down in the tunnel. Then, jump on the platforms to the box which has a heart on it. Get it and you will get an extra life. Exit the level and repeat this until you get 99 lives
During anytime in gameplay, quickly tap X and then Square to jump and whip Croc's tail. Then immediately hold X. If done correctly, Croc will begin to float for about 1 to 2 seconds. This is useful for reaching ledges.
In the board "Lights, Camel, Action", go to the room that's after the room where you save the Gobbo by the monkey bars. Stome 3 times on the first jello and you should then find a secret room with 4 hearts.
Press select while on the audio options screen to goto the sound test.