Butterfly
Slash cancelled into a dash, over and over, so you never stop moving.
DifficultyNever really finished
What it does
The technique the whole game is named for, in practice. Each slash is interrupted by a dash before its recovery finishes, and each dash is interrupted by the next slash. The result is continuous lateral movement with a sword swinging through it — you are attacking and dodging on the same inputs, and you are never standing still long enough to be an easy target.
Why it exists in the code
A dash and a sword swing are separate animation states, and the original code lets the dash take over from the slash before the slash has finished playing. That override was never removed, so the recovery frames of a slash are effectively optional if you have another input ready. Nothing about this was designed; it was found, and then it became the game.
This behaviour is preserved deliberately. It is not on a list of things to fix.
The mistake everyone makes first
Rushing the second input. If the slash has not started, the dash simply replaces it and you get movement with no attack. The rhythm is slower than it looks in a montage — start deliberately slow, alternate cleanly, and let the speed arrive on its own.