In The Soldiers Tale, after the Soldier defeats the Devil to Save the Princess, the Devil leaves him with a warning that his victory will be undone if he ever leaves the kingdom. At the Princess's insistence, the Soldier decides to go back to his home village in search of his mother. Cue the final number: "Triumphal March of the Devil."
In The Black Rider, the bookish Wilhelm makes a deal with Peg Leg, a forest-dwelling hermit, to obtain magic bullets that never miss. He uses them to impress the Kaatchen's father (an avid huntsman) and win his permission to marry her. But on their wedding day, during a ceremony in which the groom shoots a wooden bird out of a tree, the bullet arcs and hits Kaatchen in the heart, killing her.
The Visit is about an elderly billionairess who returns to her struggling hometown and offers to save them from financial destruction. The only condition is that the villagers must murder her former lover, one of the foremost citizens of the town who wronged her many years before. Although the villagers initially scorn her suggestion, the temptation is too much and they do away with the man.
Arguably Theatre/Tosca. After her lover Mario is arrested for harboring a political fugitive, renowned singer Floria Tosca makes a terrible bargain with the corrupt chief of police Baron Scarpia to secure his safety. Tosca murders Scarpia before he can rape her, only to discover that he'd had no intention of upholding his bargain. Mario is executed by firing squad and the now-wanted Tosca leaps from the parapet of the fortress in despair before Scarpia's men can arrest her for his murder. Scarpia may be dead, but the totalitarian regime he represents is still in power. All of its political opposition is dead or in hiding, and Tosca and Mario are both dead.