Wait approximately twenty seconds after the end of the credits to see the final ending.
Find all eight Master's Emblems located in various areas throughout the game, then go the northwestern area of GreenWood and speak with the Fairy Gem to earn the Magic Bell, an item which prevents your magic spells from using Gems.
Go to the screen where Death Toll's castle is located (where you obtained The Soul Blade), but do not go anywhere. As soon as you get to this screen, there will be two Rolling Squares on each side of you, and one ahead of you. To defeat all of these Rolling Squares, face forward, and move up slightly so that you are between them. Then, still facing forward, press B to use your Phoenix Power. To use this Power, you need the Soul Blade and Armor, plus the Phoenix Magic which you get by collecting the 'Red-Hot Items''. Repeat this process until you are at Level 35, or higher to be as strong as a Boss