This is a really good plugin in general! It adds a lot of style (and saves me time on drawing walkarounds, hehe)
I found a small bug in the MV version, at least. I tried it with all the other plugins turned off, but it wasn't a totally sanitized project so it's possible it may have just been on my end.
Bug behavior was, if you just started a new game and the flag for flipping on Y movement is off, moving left and right has no flipping effect until a vertical direction is pressed, at which point the flipping works from that point onward.
After rummaging around in the code I thiiiink (I know almost nothing about code, so sorry if this is inaccurate) this is due to the prevVerticalDirection variable throwing off a calculation when it is in an uninitialized or unpopulated state; I'm not sure what the default behavior of that is like in MV. If I had to make a shot in the dark, I thiiiink it might be line 170 not digesting properly, but am not able to determine that.
I resolved the issue by adding the following as line 81:
"this._prevVerticalDirection = 2;"
Which initializes prevVerticalDirection with usable input, and with that in place the horizontal sprite flipping functions as expected right off the bat. I tried it equal to 1 first and the problem persisted, which is why I think its uninitialized state is throwing off a calculation somewhere, but again, pure fancy on my end.
If no one else encounters this problem, I guess it's just me, but if anyone else does, that might patch it up. Oh, and the script version I am using is V 1.0 (initial release).
Anyway anyway, thank you for making this plugin and for all the others too! I've been buying all the ones I can and I'm super wowed by the functionality, will be keeping an eye on stuff as it comes out! ^^