Mordred returns to series 5 - but not how u think 

When i found this out, it spoiled my whole week.
Asa forever!

yeah, I feel the same. I want old Mordred and I don't care it's been 5 years

The news made me happy. It means that there's another time skip. Merlin's been at Camelot for about 7-8 years (maybe even a decade!) since that Wednesday when he met Gaius in adjusted mean Merlin Time (I wonder if they'll have a cake?). So, we'll see how much or how little progress Merlin's made. And, I doubt he's made any!

If he stays a manservant then it's likely Merlin will embrace the Dark Side becoming "DARK" Merlin taking on more and more villainous characteristics during the Season until he will become the Anti-Hero! That will make it very likely that he will fail, as all Anti-Hero must do, to finish his Hero's Journey.

If that happens then a "twist and turn" in this version of the Arthurian legend would include the high likelihood that Mordred kills either directly or indirectly Merlin instead of Arthur and thus, preventing Merlin from fulfilling his destiny as Khilgarrah predicted when he warned Merlin against helping the Druid boy in Season 1.

And, I think that that will be interesting to watch! Because, there will be a true cliff hanger as the Season and series finale comes to and end. Who will Mordred kill or cause to be killed: Merlin or Arthur?