I'll start with what i disliked:
some masks lasks blending/integration (0:20 the sequence were she walks around differents landscape, the masks are evident and lacks a bit of feathering. 2:03: avoid using masks of a character when the background stills have this character. it's confusing). others lacks realism( like the last one i said at 2:03 . there's also the one at 0:11 with the running girl: you shift dimensions and it's harsh for the eye this way, there's a too big different difference of lights/contrat/colors). When making a mask, make sure it helps your dynamism, that it's relevant to use it.
for gestion of rythm/sync, it wasn't too bad. But some scenes ( decapitation at 0:54 and others during the main fight (1:55 and 1:37 for example)) lacks a lot of movement. they're too static for the sequence you have, compared to others scenes before and after. trying to always put a little traveling/zoom (nothing big, just to make it move a bit) will really help you rythm and movements.
As for the rest, your end leaves to a possible sequel, and i manage to understand your story (I think). I noticed your getting better with the time, and i'll be interested to see your next one.
Oh thanks for sending your amv to g-anime