outside of the polar star, rocket launcher, fireball, machine gun and sword, there are four more weapons that you can find--here's how, and why you might want them. (all descriptions are in my own words--I'll only list damage if I know it--sorry!)
1. the bubbline
•how-when you get jellyfish juice from bushlands, go back to mimiga village and use it on the fireplace in the meeting hall--presto! bubbline.
•description-lvl 1...fires a slow, short range bubble.-1 damage
-lvl 2...fires faster moving bubbles like a machine gun.-2 damage per bubble
-max lvl...fires bubbles that hover around you like a shield and shoot projectile when you stop firing in the direction you are facing.-2 damage per bubble/shot
2. the snake
•how-trade the polar star & fireball to labyrinth vendor
•description-fires through walls
-lvl 1...fires a short range projectile.-3 damage
-lvl 2...fires a longer ranged projectile through walls.-4 damage
-max lvl...fires an even longer range projectile that passes through walls.-6 damage
3. the nemesis...personally, I don't like this weapon at all because it essentially levels DOWN; and faster than every other gun in the game.
•how-when you get to kazuma on the outer wall, jump down and immediately boost to the left into the opening. (I got so p***** off at this; it is an extremely HARD jump.) go down to the door but be careful of the hole in the floor. talk to the little people there. when one asks if you've seen her husband, leave (being careful of the first hole) and boost back up to the wall. go back to mimiga cemetary and look VERY carefully for another tiny man in green. talk to him and bring him back to the other littles. then talk to him when you get there (he automatically leaves your inventory) and he will trade the nemesis for the blade. if you don't like it, talk to him again and he will trade back the blade.
•description-lvl 1...fires a fast projectile long distances that passes through enemies.-12 damage {see Pt. 2}