Before you turn on your game, insert your controller into the second slot. When you turn on game, press start. You'll start on a random level.

At option screen, press right, A, B, C, start. You will hear Adult Simba roar, confirming the code.

When you go down the first waterfall in the Hakunamatata Stage, hold right to go to an easier path.

In the stage with lava, you will pass by a big wall. Go through the wall and get the item inside. In the last part of that stage, there are holes which shoot fire towards the ceiling.

To pass this, wait until parts of the ceiling clog all the holes. When all the holes are clogged, go to the one on the very right and stay on top of it. It'll give you a boost to the next stage.

At the Options screen, press Right, A, A, B, Start. Two new options will appear.

Go to level 1 and find where the extra man. Roll under so you go further down and get the continue. Now get all the bugs on this level that make your energy bar and roar bar bigger. Then die until you have to use a continue. Repeat this a few times and you will max out your roar bar and energy bar.