Super Cheat
Start the game, enter any area and press Start to pause. Press Select 16 times to make a cursor appear on your number of lives. Then simultaneously hold A and B, and move the cursor box left or right. When you get the cursor over a number you wish to change, press Up or Down. If you put the cursor on the Wario face at the bottom left and un-pause, you'll get a better hat.

Unlimited Coins
When playing, press START. Then press SELECT 16 times. When you see a flashing square on the last digit of your lives, press A and B and move the square to the number of coins and press up or down depending on how many coins you want.

Unlimited lives
When you are playing warioland push "START",then push 16 times on "SELECT", now you see a cursor at your lives, you can move it by pressing A and a arrow of by pressing B and a arrow