Deus ex machina
It seems lately that the Deus Ex Machina has been called out by many as a lazy trope to solve all the problems of a script but in into original conception it is not.
Aeschylus probably used it first in the Libation Bearers when he rolled the furies out on the stage pulled on a cart on through an open door. It should be noted that the audience of the Dionysian festival would have believed or at least conceptualized the furies as real, they had a meaning and the plot of the trilogy hinged on the furies chasing the matricide, Orestes to Athens for his trial with Athena. Where blood guilt is forgiven and the Furies (the kindly ones) are appeased. The first use of the deus ex machina was to bring true physical and dramatic horror of the monstrous and awe awaking to the stage. The audience again was indoctrinated in the story and felt the horror. A modern parallel is the xenomorph in Alien and Aliens a monster with superhuman powers that devours us from within and incorporates part of us, it hides in our innards waiting to be born out tearing us apart and becoming an external threat also.
Euripides was the most famous for its use and was the first criticized for it. He has several examples but I have two that show his brilliant utilization of it. One is the chariot of dragons that sweeps Medea away. She has just been a filicide by murdering her two sons , a regicide murdering and king and his daughter. But when Jason comes for revenge the chariot appears to whisk her away. This is a satisfying end because Medea has used darkness of her soul and her craft and naivety of others to accomplish the murder. Then she calls on her familial gods for an escape. It showed the Greeks that the gods can be dark, and facilitate vengeance and injustice. Medea is a monster conflicted but in the end committed to horrible vengeance and sacrifice for it. She has called on the darkest part of the divine in herself and the world to achieve her aims. Her escape again is feasible to the Greeks, they would have been primed in mythos for her escape. Evil seeds deeper evil that shocks us. Justice is not automatic and we often understandingly escape with our jealousy and vengeance intact and are carried off into our own dark ends. This would have been stunning it its day as it required a crane like devise and was technically equivalent to the best special effect ever in a play. It was part of the story it fit, it was tied to the mythos and themes of the play and Medea was able to call on the darkest things in its nature. It reminds me of Vader in star wars who can do the extraordinary in all aspect, who controls things by harnessing the darkness. (Note: Euripides scored third place (last place in the competition ) so this is a third rate play to the Greeks LOL)
The crane was used again in Orestes by Euripides. He creates a troupe of murderous aristocrats who are out of a favor for Orestes matricide (as revenge for his mother the queen killing his father.) Orestes is tormented by the Furies and as the city of Argos wishes to kill him or exile him he decides to murder the daughter of Helen, Hermione and burn the city to the ground. Orestes is not like Aeschylus version, who is tried by Athena and Apollo in a nice satisfying ending. Electra his sister and his best friend are about to complete the gotterdammerung murder suicide when Apollo is lifted up on the crane and tells everyone to put down their knives and torches and head to Athens for the Trial with him and Athena where they will be expunged of guilt. Hermione will marry Orestes (who is currently about to slit her throat) and his friend will marry Electra and things will be happily ever after. This is Euripides commenting on the Orestia by Aeschylus. He is mocking the easy wrapping up of a plot where the gods solve all the problems by showing how ridiculous it is for the gods to solve all things in your favor. Euripides mocked Sophocles and Aeschylus for flaws in their plays by mocking or using their devices in the extreme. His deus ex machina was brilliant.
The best recent use was in Mighty Aphrodite where Woody Allens gods are silly stage gods and the heroine is saved by a helicopter pilot when her car dies in the middle of nowhere. Allen breaks the four wall and call out that he is using the Deus Ex Machina, even if the savior is just a man in a machine. Allen with a little joke makes a larger joke solves a big plot hole by owning up to what he is doing. The Deus Ex Machina can be used well, but I don’t deny that it can be used poorly and lazily to fill plot holes.