You need to attack when the stamina bar is fully charged, otherwise you do reduced damaged. A good strategy is to attack, then back off and wait for the stamina bar to charge, then move in and attack again; repeat until it's dead. You also generally want to strafe around to the back of enemies while using a combination of attacking and magic to stunlock them.
~ ® Indie RPG developer.
Twitter: twitter.com/JC_Bailey1112
Twitter: twitter.com/JC_Bailey1112