Unlock Bonus dungeon:
Finish the game. Following the credit sequence, you can  continue playing and go to the Dragon Fountain, when you reach this fountain push A to play the New Land dungeon.

Unlock Mountain level:
Finish the Light House level.

Defeat the L-Marshy (Lighthouse Boss):
First you have to beat Marshy. After you defeat Marshy, L-Marshy will appear. Begin the assault with normal strikes with a strong weapon (important).

Defeat the  Loboss (Forest Boss):
You can beat the Loboss very easily but his henchmen are a little more difficult. The henchmen have good HP, defense, and power. You can use a good weapon that can hit them more than once at the same time. You can use this same strategy when facing Loboss.

Get the clown suit:
After you finish the circus level go to the house that is near your house. Talk to the girl and she will say "I picked this out at the circus." You have now received the clown suit.

Get Thunder:
To get the Thunder weapon, get a Cannon and a Moon Bow. Combine these items to receive thunder

How to make X-Sword:
After you unlock the Blacksmith shop (following the completion of the circus level) get a G-Bow and Red Sword there. If you return to the blacksmith to combine the two items to get the X-sword (G-bow then Red Sword) This is expensive, but well worth your troubles.