5 Extra Lives
When on the title screen, hold Down, A + B and press Start.
Continue later in game
When you are playing a 2 player game, and one player loses all his lifes, do NOT continue the game, then continue on. When you reach the point your partner wants to continue on, have him press START on the map screen. He will come back, even after his absence!
Extra Continues in a One Player Game
Start a two player game. Now, beat up Zitz until all of his lives are gone. When you're given the chance to continue, don't. Now play the game normally as Rash, and when you get a game over as him, press start on controller 2, so you'll play as Zitz. Again, when you're defeated as him, press start on controller 1 and you'll resume play as Rash. By repeating this, you'll have more than 3 continues in a solo game!
Start later in a 2-player game
A variation of the continue later code for 2 player games in Nintendo power I discovered myself. Rather simple....
Start a 1-player game and proceed to whatever level you wish. When you get to the level your friend wants to start in (you could go to level 9 and play that when your inexperienced friend couldn't make it there, for example) You will then start with all continues/lives and start on the level 1P is currently on!
Warp to Level 3
When you begin the game, quickly headbutt the psyko pig on the left, then the one on the right, proceed to where the Walker appears, you should see a platform and a pulsating warp. Jump up there quickly!!!
Warp to Level 5
In Level 3 (The turbo tunnel) in the last section of the speed bike obstacle course (where the walls pass REALLY fast) slam headfirst into the 10th wall. That should be a warp. (The correct wall is on the bottom of the island BTW)
Warp to Level 6
In Level 4 (Ice Caverns) when you find the platform that falls when you stand on it, go down near the bottom, then jump repeatedly so it goes back up. There should be a warp formed at the top.
Warp to Level 8
In Level 6 (Karnaths Lair) in the 2nd Snake pit, climb on the first snake and jump all the way to the right when the snake reaches the height of it's path (don't hit the spikes) there should be a warp on the other side. You must jump over because the warp will disappear before the snake gets there.