B skips “cutscene series” while A only skips an element of the series.
Shuriken changes jump
Throwing a shuriken alters your Y position. Depending on when you throw, you can either increase it or reduce it slightly. Can be used to land earlier (jump length dependent) and to jump earlier beneath a ceiling.
Weapon menu glitch
If you move while pressing select, you can get closer to the side of the level (required to OoB). Found by igorsson, clicky for video. This is much faster than entering a door and exiting. Requires to move at least for 1 frame before pressing select.
Direction change in air
Generally you need to wait a lot of time to change your direction and go full speed (1px/f constant). If you hit a wall, you will move with 1px/f instantly.
Optimal direction change on ground after jump
You need to wait 1 frame before the next jump, so you are able to turn around and go with 1px/f.
Optimal jumping down
If you make a flip jump before jumping down a platform, you will get horizontal speed increment earlier. Also moving left for 1 frame before a few frames can squeeze out +1 X position.
Damage dealing tricks
Use knife when possible (attack very close)
If you hit an enemy on the boundary of his hitbox, you will damage 2 instead 1 (knife instead shuriken). Works on everyone except 1st boss (well it's actually works but you can only hit his 2nd hitbox which doesn't changes boss health).
Art of the Shadow
The imitate ninja (upper one) has 1 frame advantage (faster) to damage enemies on Boss 1. Even if the shurikens have same X positions.
(TODO: sometimes it's the opposite)
Out of bounds tricks
You can go through walls if your X positions is at least 246 pixels.
Fix horizontal OoB stuck
You need to make a simple jump. This happens when you start OoB on a really high Y pos. Currently it's faster then lowering Y position to avoid stucking/jumping.
Fall through tiles
With enough X positions (246?), you can fall through tiles, but it's also Y position dependent (when you "collide" with that wall you are about to go through).
Camera rules and tricks
The camera only scrolls horizontally if your X position is less than 248 and the camera reached the end of the screen vertically.
The camera only scrolls vertically if the camera reached the screen's end horizontally.
You can bypass the "screen-to-screen" transitions if your Y velocity is at least 3 and your Y position is very near to the top of the screen (so your head isn't visible).
End of screen transition
The camera has 1px/f speed, so the ninja will be transitioned with that speed. Therefore you need to start the camera scrolling as soon as possible so you won't need to wait for the remaining transition later.
Scripted transitions (after flying)
You can squeeze out a few X/Y position if you don't go through the transition' boundary (which would otherwise send you back many pixels away).
Depends on entering the level on an even or odd frame. It's usually only changes minimal things like jumping a few frames later.
Boss 1 brick
Depends on X position.
Boss 2 strategy
The 3 ninja represents the bottom 3 stones. The fourth one spawns when the 3 stones get 5 dmg (max health).
Elaborate boss 2-3-4-5 things
Saved 1 frame, magically reduced loading time with an additional 1 frame before boss 2. explanation?