Sorcerer
You must defeat an evil sorcerer to clear the Forest Shrine level. The sorcerer hovers in the center of the room with his crystal ball and shoots lightning at you while also summoning poisonous blobs. You need to cross three moving platforms just to reach him, so the best strategy involves standing on the ledge just inside the door and firing bows at the sorcerer. Come equipped with enough bows and you won't even have to deal with the platforms.
Spirit
The boss at the end of the Non-Entity's Cave is a three-eyed spirit that floats across the top of the screen while attempting to capture you in vortexes. The spirit also summons meteor showers, which can inflict serious damage if you're snared in a vortex. Stay clear of the vortexes and watch for shadows on the ground, as they indicate falling meteors. Fire your armlet beam into one of the spirit's two lower eyes, which in turn causes it to open its third eye. Jump up and slash the open third eye to inflict damage. Keep repeating the same process to claim victory, but beware of the third eye shooting a laser towards the end of the fight.
Silver Armlet
At the end of the game's final level, Agito's Castle, you come face to face with the ultimate enemy, Silver Armlet. A mysterious hooded figure, Silver Armlet calls upon an ogre, a raptor, a swordsman and an elite knight to do battle. Use the Death Sword or some similarly powerful weapon and take the battle to Silver Armlet's minions, hacking them to pieces. Silver Armlet attacks with shurikens, knives, a whip-like weapon and a flashing light maneuver that can be devastating. Concentrate on Silver Armlet at all times, as the assorted minions serve to confuse and distract but don't pose much of a threat. When you see Silver Armlet levitate, it means the light attack is on its way. That's when you need to attack, because Silver Armlet will be vulnerable while hovering. Keep hacking away until you achieve victory.
Agito
After losing, Silver Armlet admits defeat before sprinting into the next room and summoning Agito, a gigantic green monster that takes up most of the screen. Agito attacks with energy-shooting tentacles and explosive slime that rise up from watery areas on either side of the screen. Run back and forth to hack each tentacle to shreds, which prompts Agito to extend his head, leaving him vulnerable for jumping kicks and slashes. Be careful if you see Agito close his eyes, because it means he's about to spit fire. Keep repeating the same process of slashing tentacles and then targeting Agito's head until the behemoth dies.