Since it's been revealed that Mordred will be a knight of Camelot, I wondered how is the show going to pull it off? Since Arthur made a pact with the Druids in season 4, would Mordred be allowed to become a knight by going through the trials like the others? Everyone will know that Mordred has magic and maybe letting him join would show Camelot's magical community that Arthur is not Uther, and neutralize any potential alliances from that group with Morgana.
Mordred is by Arthur's side a lot, a fact that would really burn Merlin. But for Mordred to get so close, he would to have to perform a feat that would win Arthur's gratitude. My guess (and hope) is that Mordred uses his powers to reveal that Morgana used magic to set up Guinevere to betray Arthur. Merlin would be beside himself because he didn't use his abilities to clear Gwen's name, and he knows of the prophecy that Mordred will kill Arthur. Merlin can't go into details without exposing his own magic; and that's a bad thing. If someone finds out about Merlin and exposed him, namely Mordred, Merlin would have a lot of explaining to do: not coming clean about what he was and hiding the truth for so long is going to be a tough row to hoe. Gaius would go down too because he knew from the very beginning.
The scary part of this is that Mordred could have his own agenda. Eliminating Merlin and possibly Gaius from having any influence on the king is step 1. He could also be a a mole for Morgana (again?!), but he could play both sides against each other. (That would explain how Morgana escaped in the last episode of season 4.) Mordred could want Arthur to fall and claim Camelot for himself by using Morgana's blind hatred as a weapon. He may allow Morgana to think he's siding with her so she can reclaim the throne for the umpteenth time. Morgana's vision last season about a great battle - Camelot vs. Morgana, Mordred and a new army (Saxons?) - where she's begging Emyrs/Merlin to help her. It's a good chance Mordred turns on Morgana and runs her through. Mordred got Arthur (maybe?), Camelot is taken, and to keep control of the kingdom Mordred claims the lawful queen, Guinevere. Morgana, the royal bastard, is of no further use so Mordred dispatches her. Another interesting wrinkle is the Aithusa/Morgana connection. From an earlier post I said Morgana may be a dragonlady that controls Aithusa, but what if it's Mordred who is the dragonlord? Mordred could be instructing Aithusa to obey Morgana, letting her think it's her ally. There will be a crucial moment where the dragon refuse to obey Morgana but will obey Mordred. That's when Morgana learns she was double-crossed. I hate to say it, but if Mordred orders Aithusa to kill Morgana by roasting her I would cheer.
Well, this is what I think. I'd like to hear your imput.