Are we talking about the thing with Snow and Charming that didn’t happen? I don’t seem to recall any of the baby snatching or transferring darkness you all are talking about.
The stuff with Maleficient. Stealing her baby, putting Emma’s darkness into her (Lilly). Lilly then getting sucked into a portal with Ursula and Cruella to the real world. The author manipulated it by writing what he wanted and what he thought would make a better story. Although as Matthew Paul explained, Snow and Charming were still somehow in control of their actions. Not sure how that’s possible if someone is writing your actions, but ok.