Begin a new game in arcade mode, then on the character selection screen, press and hold Down + Left at once. Next, while still keeping the previous buttons held down, press the A + C + Start buttons at once. If the code was entered correctly, when you lose all your lives during gameplay you can continue from the Game Over screen with 9 credits.
1) If you are fighting enemies and they are near an edge then if you jump up and hit them and knock them off you will save yourself a lot of time. This is especially handy at the final part of the dungeon level
2) Save your magic and don't use it unless it's on boss characters. Also try and save up for your maximum amount of magic and only use it on boss characters to deal tons of damage
3) Mount an animal whenever you can because when you are knocked off you will take no damage
4) Learn the attack patterns of Death Adder and you'll know when he's about to unleash his most powerful attack
Select Arcade Mode, then hold down/left and B and press start at the character selection screen. A number which corresponds to the starting level will appear. Press up or down to change the level.