Instructions
Open the WC3 Map Editor and load a map, either your own or a default "Warcraft III" map.
Click on the "Object Editor" and select the "Abilities" tab. Create a new ability and name it "Attack1" and click "OK."
Open the tab named "Art-Animation Names" and select the new ability's animation. Click the arrow key to scroll through different animations for that unit.
Type in the animation title in the description box and click "OK" to save it.
Give that new skill to a unit to give it the attack animation.