I dunnow if I'm in any position to give you advice
but:
-the fight between umaro and mog: glitch at the end: you should put your layers in this order: background - blood - character, self explanatory
Vertically shrink the mog sprite when it gets crushed
-the fight between sephiroth and Kefka: don't move the lower half of the body, you should only move the parts that are sliced off
-blood: big mistake using a regular shapes(circles, ovals) make it somwhat more irregular, but avoid sharp angles, perhaps use shape tweens
-backgrounds: too simple: place a few objects that can be used in the fight such as rock formations, crates, other obstacles.
-try looping your music
That's all I have to say