Unlock the Blacksmith shop (after the circus level) and get a G-Bow and a Red Sword there. Go to the Blacksmith and combine the two, first using the G-Bow. It is expensive, but worth it. You can use the X-Sword to get better weapons. You can also use it to get the XX-Sword.
Get a trapper and some food. Go to any level except the town. Find some monsters and select the "Option" button. Select "Items" then choose "Trapper". It will say "Add bait". Select "Yes". Leave the trap for a little while and the game will respond," It seems that a monster has gotten into your trap". Go there and fight the monster. Defeat the monster and say "Yes" so that it will join you. They each have different attacks.