Jessica's redux murder spree in Season 13 (per DVD count) should have been played absolutely straight, like a horror movie, and (as others have suggested) should have been directed at the Dallas cartel we knew but were not really appearing much anymore (instead of Clayton's business associates with whom we were unfamiliar). It would turn out that Jessica had been blackmailing most of the cartel over Dusty's parentage, her scamming them all for 40 years that they were all his biological daddies (like Kristen did with Jordan Lee), and Jessica turned vengeful once they all ceased payment upon her entry into the asylum following her kidnapping of Miss Ellie and driving her to Loredo in the trunk of that town car.
Now, that's a constructive use of killing characters, even if we didn't know the cartel all that well. Only Marilee Stone (injured and now vengeful towards the Ewings, though attention from an unmarried Bobby might help) and Jordan Lee (who lives to die another day in Paris) survives.
Method of murder? I say: go for the axe... No absurd fish-tank dunkings.