I'm pretty sure the default attack animation is the simple your hero goes "Augh!" But you can go into skills, make an "attack" skill of your own with an animation you like (Maybe spear 2 or something, or one you make yourself) and damage equal to what you want it to be, then under the monster tab, change the normal "Attack" function to the attack with the animation you set up.
I actually haven't tried this, but it works fine in my head