So here are some of the advanced techniques I discovered while TASing this game.
The first one I like to call eastwood shooting. If you don't get the reference then go watch this:
https://www.youtube.com/watch?v=mkr0bwV5YWE
So, what this trick does is allow a shot to be fired every 3 frames. It's perfect for decimating bosses but hinders all movement so it shouldn't be done while moving in levels except for very specific situations.
To do the trick you must shoot, then wait a frame, then turn in a different direction (to cancel the animation), then turn back, then shoot, then turn etc..
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The next trick I discovered is pretty simple but useful. I guess we'll call it shot hovering. What it does is give you a little extra distance while in the air to make otherwise impossible jumps. To do it, simply jump and reach your max height and start to descend, then fire a shot. You will hover very slightly but it does make a big difference sometimes.
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The last and easily most useful technique I discovered is quick shooting. It is used to get out shots really quickly without having to slowdown or lose speed. When quick shooting you pretty much become a train and your bullets are your plow.
What is done is, you shoot then jump for 1 frame. Jumping cancels the shooting animation so while in the air you can shoot again. Then the moment you land you shoot again and repeat. This allows you to destroy enemies very quickly without ever slowing down!