If the victim is truly helpless, then they can just kill them with no roll necessary. Common sense should always trump the rules.

If the victim is truly helpless, then they can just kill them with no roll necessary. Common sense should always trump the rules. (Basic Rules, p. 4)

1. The DM describes the environment.
2. The players describe what they want to do.
3. The DM narrates the results of the adventurers’ actions.