Collect all 3 Cortex tokens to access Cortex's Bonus Round.
Token 1 - After the second major ascending section, you will reach a checkpoint that houses an outline of boxes behind you. You'll notice a metal "!" box above you and a red lizard ahead that'll start jumping at you. Lure the lizard back some until he is underneath a metal "!" box. Bounce off the lizard and hit that metal "!" box. It'll cause the white outlined boxes to become breakable and the first token is in those set of boxes.
Token 2 - Very shortly after the first token, you come across a set of four walls that'll push out followed by two lone boxes. The second box is slightly hovering above ground. What you'll need to do is to bounce off the two boxes and jump on top of the following set of walls where the second Cortex Token is located.
Token 3 - Right before the Cortex Bonus Room Teleporter, you'll be on two sets of three rotating platforms, you'll see a lone life randomly sitting in the back of a ruin. Jump to that life and go left to find a very well hidden box that houses the final Cortex Token.
The Cortex bonus pad is nearby. You must get to the end for the key. If you die here you won't lose a life so keep trying!
After you complete the bonus round you will need to make it to the end of the level to unlock the trophy.