Prophecy:
In a maze there lives a bed of lies,
Six must face them to regain lost ties.
A daughter of love or of strife,
Shall faced the end of a cursed knife.
The pit or the grain's daughter,
Will see meaningless slaughter.
The son of power shall make a decision,
And the banished one will come with a vision.

The maze is the labyrinth mentioned in BoO, when Hazel and Pasaphe battle...if you call it that.
The banished one is Apollo, and the decision will either be about sacrificing himself, or about girls, or about wether or not to do something that decides if they finish the quest successfully.
The slaughter thing I'm not sure about...but the lies might be a sort of hallucination they experience and have to overcome lies they are told in it or possibly just find a way out of the hallucination, or maybe even having someone in the group lying to everyone else.
I think the cursed knife will be what kills one of the two mentioned, that way if Power's son sacrifices himself, and one person can't overcome the lies, only 3 make it back from the quest like usually would.