Coracle, is this the NZ series you mentioned?
It looks interesting. Is it based on a Maori legend?

http://www.kaitangatatwitch.co.nz/index.html

Yes. It's by famous local author Margaret Mahy, haven't found out whether it's based on any legend. (not a familiar one)

[Off topic: It was filmed about a year ago, in Governors Bay where Mahy lives! I know the man playing the father of the blonde boy - he's a local actor/director/teacher.
The old Maori man is played by a famous NZ actor.
A London-based NZ-born friend of mine did makeup. And in one of the episodes the girl is wearing pyjamas exactly the same as a pair I have!!]
Back to the topic....

Coriakin a villian? I don't think that's happening! what in the trailer makes you think he's a villian?

I don't think he's going to be a villain, but the marketing may try to pose him as a menacing figure, so that when you watch the movie you may wonder whether he is evil or not (after all, when you read the book for the first time, from Lucy and the Duffer's perspectives he seems evil).

As for taking over Ramandu's position, it's possible. I wouldn't like it, but so far it seems like Ramandu may not be in this movie at all; we haven't heard a single peep about him. I was thinking that RD's (er, Lilliandil's) character might merge with Ramandu's, but the idea of Coriakin taking that position is possible as well. Still, I'd rather they just left Ramandu in... he was so very different than Coriakin; more regal and distinguished, less mysterious and, well, freaky.

Coriakin taking the role of Ramandu? Is that even possible? I thought someone had been cast as Ramandu....

Nope, we've had no word on a Ramandu casting as yet, and no other variety of confirmation that he will be in the movie.

There was an early piece of concept art in the background of a production member's photo that was apparently titled "Ramandu's Island", but as I said, it is likely a very early work and proves nothing.

He may have seemed intimidating in the trailer. But intimidating does not automatically equal threatening- let alone evil. So while Lucy may have been startled and perhaps intimidated by Coriakin at first, I honestly do not think that his role and personality will be changed. It would greatly alter the plot if he were to be made into an antagonist to Caspian and company. None of the characters are perfect (except that Panthera leo that shows up in all 7 books)- but I truly hope Coriakin is not turned evil in any way.