LOW G MAN (no, i dont beat the last boss because i dont have an optimal strategy)
yeah, theres prolly people who know more about the game, but ill run down my experience for the hell of it.
tap forward twice to run instead of walk.
if you ever have to jump and find yourself sticking instead of moving again, try shooting, as it seems to cancel the lack of movement after a jump (this only seems to happen with small jumps, such as those that wont stick me in place as i freeze enemies).
drops seem to be manipulated by waiting a certain amount of time for an enemy to take the deathblow, but some enemies have pre-determined drop rates (such as the bombs). manipulating more S drops might or might not be best. i can see a few instances where it works well, but theres some levels you're doing more jumping than running... so im not sure.
oh, and having a double/triple shot may help in getting multiple enemies (the blue dragon-head wing thing) while the circle with wings will increase your jump (which is useful because of some vertical areas).
there are times when using the downwards spear (and perhaps upwards spear) seem to cancel out enemy attacks damaging you. theres a few boss battles like that.
im really not sure about getting special weapons. so far, the bombs were the only things i used. but then again, i wouldnt know what address to look in to determine hit points for enemies.
the boss of 2-2 (ocean descent) is a mystery to me. his movements depend on yours, so keep that in mind.
the sub-marine boss takes insane amounts of shots to freeze... jerk.
3-1 (mines) bos is an example of literally standing on him and not taking damage from him. im not even sure if killing the gunner was needed.
3-2 boss is interesting. he goes up up and away. and i think taking him to the highest point and attacking from above (which does take him higher, pixels at a time) until hes off the screen may have been what killed him. that battle was a lot longer.
3-3's one of the vertical levels. the boss is an example of the spear canceling damage.
4-1's boss is a random one. depending on your position will determine where he'll reappear (and i mean by the slightest pixel). so theres possibilites of makiing him stay in place, as million-1 as it may seem.
4-2's boss is tough. those aren't refill-your-life potions, they're poison. so handle him with caution.
5-1 only has one boss, but killing the others helps (and grouping them like that does as well).
5-2... i shouldnt have used the hovercraft so much, i thought there were only 2. in any case, it'll help you to have one in full health against the last boss of the games lower bits.
why dont i do it? i dont really have the patience. its a sort of frame specific game at points. but if you want a game to do, this ones out there.