Lancel Lannister underwent the greatest off-screen transformation of any character in the show, morphing from a hapless, bumbling squire into a composed, devout member of the Faith Militant. He played a key role in Cersei's incestuous crimes, and in bringing her deeds before the High Sparrow, so he will be sure to make an appearance in the Season 5 finale, but what sort of effect can he have on the proceedings during Cersei's trial? That is, providing her trial takes place in the finale. Lancel might not be able to match the impact he's already made on the King's Landing hierarchy after making Cersei aware of his group, which ultimately led to Queen Margaery and Loras falling into the dungeons before Cersei, while King Tommen is left isolated in the Red Keep. He will be crucial to sentencing Cersei so expect big things from him.