There has been a lot of discussion about whether Ofelia's experiences in Pan's Labyrinth are real or imaginary. But assuming they are imaginary or an unreliable narration, what are the real events that took place?
My interpretation while watching the film was that Ofelia was conscripted to run errands for the rebels by Mercedes. Pan is Mercedes; they communicated by meeting in the labyrinth or leaving messages in the notebook in the bathroom. From this Ofelia concluded Mercedes was working for the rebels. Ofelia retrieved the second copy of key that the rebels stashed in the forest and the knife from the dining room while Vidal was asleep. The rebels planned to murder Vidal's son to get revenge and needed Ofelia to bring the baby to them.
This version does not really hold up to scrutiny, though: Mercedes was carrying the knife all the time. I don't think the film reveals where the second copy of the key is held.
Del Toro said fairy tales have narratives with symbolic repetition. The key and knife being major plot elements in both the real and fantastical stories; the disobedient nature of both Mercedes and Ofelia; the chasing of Ofelia by both Vidal and the Pale Man. But if Ofelia was not working for the rebels then this is repetition only the viewer is aware of. Ofelia could not know the real events to base her tale on.