Use the following trick if you are at high levels (over level 50), have a small amount of money (less than 1000), and have a bad weapon (single shot, etc.). When you reach the shop, buy a quad shot, auto fire unit and extra bullets. Buying more extra bullets is recommended. good.
After that, hold [Fire]. It will rain lots quad shots quickly, and it will take out all enemies in three or four reloads.
The war.i.plasma weapon is the best in the game. However if you have around 3,000 to 3,500, do not buy it. If you are satisfied with the weapon you have and you do not need to buy anything else, save your money until you have over 4,500 then buy the war.i.plasma weapon. You will have an outstanding weapon, and if by mistake you will get the single shot bonus, you will have enough money to buy a good weapon instead.
If you have a weapon and are catching bonuses of the same weapon (single shot, double shot, quad shot, etc.), the weapon will be much stronger then the original. If you catch more bonuses for the same type of weapon, the weapon can get better than the next one. Note: The weapon cannot become stronger than a weapon which is two times stronger. For example, single shot cannot be stronger then triple shot, etc.