Local Celestialcest Enjoyer

Another one can be the feral Whumpee, released in a controlled environment to get rid of the enemies as a last effort

They are kept in a cage, with a muzzle and restrains, treated by the Whumper like a wild animal

They aren’t allowed to talk, but they hiss and growl at their captors, staring like they want to kill with only their eyes

They try to run and fight when let free on a mission but the Whumper is too cautious, and closes every possibility, maybe in a modern scenario making the Whumpee wear a shock collar with a tracker and a boundary that will shock them when they leave it

At last, all they can do is to eliminate the targets and return to their captors like a good boy, maybe they get sedated by the collar at the end of the mission

Or maybe they themselves aren’t that feral but are given drugs/put under a spell before the mission and lose their mind, only thinking about killing anyone near them 

The third kind is the one too scared of torture to not obey

They hate attacking others and cry each time they kill somebody, they panic, beg and hesitate but do it nonetheless

That is because Whumper has a way to take them back and punish them if they disobey

So to avoid pain and out of fear they bring pain on others, they are a coward, but they can’t help it

Or they do it because they know that if it's not them, then someone else will take their place and there’s nothing they can do to stop it