On the second stage of the third area (Pyro's Area), after the first up shaft, there is a secret area in the ceiling, in the middle of the platform. Go up the shaft and to the left. Go down the next shaft and you will have to fight 5 Sumo Guys. Once that is done, slide to the left and you will find 3 1-Ups.
99 Lives
At the main menu hold down the Left Trigger and press - Right, Right, Right, Right, Right, Right, Right.
All Power Ups
At the main menu hold down the Left Trigger and press - Right, Left, Right, Left, Right, Left, Right.
Alternate Costumes
If you want to unlock the alternate costume you have to press the next buttons in a short time (as quick as you can) UP DOWN, UP DOWN, LEFT RIGHT, LEFT RIGHT, B A.
Defeating Pyro
Jump on the wall, then jump to the top. When Pyro shoots the fire circling around him, drop just before it hits the wall then dash to him. When he shoots out the birds, stay near the wall. When they are about to hit you, double jump over and slide below them. Repeat this until they burst.
Invincibility
At the main menu hold down Left Trigger and press - Down, Up, Down, Down, Up, Down, Select.
Regenerate When Claws Are Out
At the main menu hold down the Left Trigger and press - Right, Up, Down, Right, Left, Select, Select.
Unlimited Double Jumps
Go to the Main menu and Hold down the left trigger and press - Select, Left, Up, Down, Down, Up, Down.