Touhou 17.5 Speedrun Tactic/Proof of Concept: Flandre Normal B Fast Yamame
Yamame's movement RNG for her first attack isn't nearly as important as Reimu's is, so I'm just showing what seems to work every time that it is performed correctly.
That said, Yamame's big RNG is whether she goes across the screen 4 times or 6 or more times during her second attack. While 4 times is technically optimal, since you'll always need to wait for her to come down before finishing her off anyway, getting the one-cycle on it is *exceedingly* difficult. You, as far as I can tell, *need* to hit her with the 8B as she rises right when the spell is declared, and the window for doing so is small enough that I can't guarantee hitting it via mashing. I do still mash the key a few times around when I know I need to press it, since it can't hurt anything, but timing is still important. Needing to hit the 8A is also why I finish Yamame's first attack with Flandre's normal attacks, instead of using C which finishes the attack slightly faster, but almost always puts Yamame too far away.
During Yamame's last attack, that hit I took after she came down the first time was intentional, to refill my meter. That must be done in order to get to the other side of the screen fast enough with enough meter to use C twice. If your timing is better than mine was here, you can actually finish her off before she even goes to the middle of the screen, but it may also require a bit of good luck with the projectiles on Flandre's j8BB.