Executions - Kill Animation

I’ve seen in some gameplay there is a final execution kill when you defeat an enemy. Is this an unlockable skill?

When I defeat an enemy at the moment they just yield and I have to either let them go or carry on fighting them til they just collapse and die

If you knock them unconscious or if they fall to the ground of exhaustion after taking to much damage, then you can preform Mercy Kill

For most parts it’s a stop the suffering kind of deal, pretty sure they’re doomed to die anyways