Thanks for playing!
The witch is a character from a previous game of mine that never came to fruition, hence the "reused" part. That game is a bit of an in-joke, so I guess the bit doesn't really work as well out of that context. Oh well.
The slash move is most directly inspired by Specter Knight from Shovel Knight - in general the mechanics of this game are meant to pretty much just be "what if Specter of Torment was a metroidvania". I can see how it's kind of similar in functionality to Ori's bash though, so coming at it from that context I can get why you'd expect it to have a seperate bind. I haven't played the Messenger though so I dunno what the similar move there is.
The hair effect is actually really easy to create! It's just a sequence of circles that get moved around by some simple forces - mainly gravity and a drag force opposite to player motion - that then get clamped to be within a certain distance of the previous node in the chain. It gives a really nice effect without any complicated math or manual animation work at all.