Well, I actually added a new frame for a pistol (which required just a tiny bit of editing) and it worked out. Same with the whip. I just removed the knife animation for the first three attack frames and added a whip. Looks great!
As for adding animations, I think a hit frame while jumping, something like this, would be good:
Also, a running animation, if you could manage it. I think it would add an extra bit of flair to the character. Thanks for this wonderful character sprite!