Occasionally, when decapitated, enemies will lose their heads and continue fighting. It is unknown how the glitch is triggered or why it happens, but it may be due to the decapitation mechanic instantly killing enemies, and, because of coding errors, the decapitation will not kill entities.
It can only be triggered when a player decapitates an enemy with a light attack on the ground. It is not entirely sure how much health enemies need to have in order to be decapitated, but if your light attack does more damage than the amount of health enemy has, the enemy will surely be decapitated. Players can decapitate enemies that have more health than their light attack damage at times, though.
This glitch can be triggered in older versions of the game on players via the campaign arenas. The player must have at least 1 potion. The player who will lose their head must have the potion in order to work. The other player must decapitate the enemy player. The decapitated player has less than a split second to use the potion for the glitch to work. If done correctly, the player will be walking around headless.