Some Useful Tips
Some bosses can make you quit game but here is a quick guide of progression.
First, I recommend 8 way shot (red bottle in shop), and the normal peashot, fight the botanic, it is not that hard, be careful with the potato and try to parry everything you can, the onion is not that hard, you will need to look at the sky everytime, since tears could kill u, and the carrot is hard, you will need to use the 8 way, and shoot the following carrots, the lasers are easy to get trough, just see whenever one is lauched.
Then go to fight the 2 frogs (do not remember its name), use peashot and 8 way, use 8 way in first phase, also in 2nd, but in third use peashot, the third phase is incredibly hard, practice all possible attacks, the orange is the hardest.
The fight slime ball, use smoke granade dash, it is incredibly helpful, use peashot and the following shots (green bottle in the shop), peashot in 1 and 2 phase, in 3 use following shots.
Then fight the flying lady (Hilda Berg I think), and try going small whenever going through a large distance, last phase, try parrying and going through the UFO fast.
Then the flower power, parrying is the virtue in here, never, never stop parrying and shooting the little enemies the flower spawns, but There is no recommendation in here, try getting sugar cubes, easy to parry, auto parry, but do not use 8 way, short range.