Physics, Physics.
"Move every joint in every frame a bit, or at least try to."
When he smashes the sword, the only thing that moves is his arm, and thats not how you handle a big sword, so:
-Make his legs walk a bit when he smashes, because its a heavy sword he would get unbalanced.
-make his back bend, kinda same reasons as above.
-make his arms move more realistic to.
-work on the jump at the beginning and the salto.
its also a bit choppy, but better than your other ones.