You go 1px/f walking, 1.5px/f with "speed" mode (select) and 2.0px/f on downward slopes (0.5px/f on upward slopes)
Falling down right from the edge of a platform disables speed gain for 1 frame. You should always jump off from platforms.
You can also fall down right on a dead enemy (while falling down), resulting in the same (no speed for 1 frame) effect.
Game tracks subpixel positions. Only enemies has subpixel overcarry (TODO, check between levels too!)
Fastest fire/rate is every 3rd frame (B, empty, empty).
Number of lag frames on a level changes "cut scene" lag frames, you need to manually test the best lag route.
The RPS RNG depends on the cutscene start's frame and it's advancing (A) frame. Additional rounds doesn't alter the time because of the final delay on these events.
B+U - vertically slower movement (flying).
B+D - parasol bumping. You need to be above the enemy when colliding and a bit close to his hitbox horizontal wise to avoid taking damage.
You also jump after killing an enemy or contacting with the platform after B+D, refereshing your (15 max) jump meter (the vertical length of the jump).
Jump meter checks A for maximum 15 frames
Smallest jump is A (= A,A,A,A,A), any more A buttons within 10 frames will delay the vertical (subpos) speed reduction towards the apex of the jump.
While there's a maximum jump height, there are plenty variations for manipulating Y subpos through out a single jump.
Optimal lag reduction techniques
"Rapid" ( > 1.5px/f) scrolling speed usually generates a lag frame (for drawing new objects and animating them). Depending on the scenario, you could manipulate it away with specific subposes (for enemies) or timing the killing of enemies/projectiles.
Try to avoid drawing objects on the same row or column of other objects.
Not killing enemies can be favoured when there's 3 or more enemies in the same horizontal/vertical plane.