This might get a bit detailed but please stick with with me. When you got your opponents health down low, you would be able to pull off a finishing move. They wouldn't be as likely to hit, does the same damage as a normal attack, but you get some extra XP, maybe 10% or whatever would work.
Your alignment decides what you can do. For lightsiders it would be something like chopping off an arm or leg, destroying their weapon etc. Basically disabling moves. If you are darkside then there will be some more execution/humiliation moves. Like decapitation, chopping them in half., or other painful