At the game over screen, when the character stops talking, hold Select and then press Start. This can only be done 3 times.
While playing hit A and B at the same time on the second controller. This will kill Karnov.
At the title screen, hold right, select, A, and B at the same time on controller 1. On controller 2 press A the number of times equaling which stage you want to go to. Then press start on Controller 1.
At the bottom of any ladder in the game (besides the one in your inventory) press left or right and down repeatedly. Karnov should gradually move through the floor and can access areas if they are below .