Deus Ex Machina endings are so despised that people still use the Roman term from thousands of years ago, itself a translation from the older Greek, “God Out of the Machine”.
For those who’ve just tuned in to plot geekery and tropes: Imagine a Greek play, everybody in masks under a Mediterranean blue sky. The Furies are rejoicing, the hero is trapped by his enemies, the dilemmas are unsolvable and — WHOOSH! — a crane or a trapdoor-elevator — yes, a machine — literally plonks Apollo onto the stage and He — boringly — fixes everything.
These days, the Deus Ex Machin need not be a god — it can be the king, an airstrike, friendly aliens, whatever. We still make like confused crusaders and cry “Deus Ex!” because it’s a cheat ending: unearned victory or salvation is boring, and dodges the questions raised by the story.
However, Deus Ex Machina is not the only cheat ending. It has mutant cousins that often get a free pass because they ramp up the drama. Even so, they suck the life from stories by making them less rich.
Let’s call the first, “Boss out of the Box” and take Wonder Woman as an example (not because it’s a bad movie, but because we’ve all watched it). Spoilers after the cut.