Hmm, let's try a better tagline. Yeah, I'm pretty terrible at this.

"Under Me there is evil lurking. Trust in the Signs I gave you. Do not falter."

Lilygloves suggestion is probably the best so far:
"I'm going to live as like a Narnian even if there isn't any Narnia!"

I don't think anybody can beat that...

If I could do it both legally and easily I'd just make fan trailers for all seven... but I can't (yet )

How about...

"A strange new world... A quest to find the lost heir... an adventure beyond their wildest dreams...

...and it all started as a normal school day..."

Short version:

"It all started as a normal school day...."

A lady in green...a lost Prince.....a magical quest begins...
The Silver Chair - December 2061

Yay people like my suggestion! I think something like that could work. Maybe they could shorten it or find another way to rephrase it because, I don't know, it just feels awkward for me to say as a tagline. I know it doesn't have to be super short but I feel like it should be shorter.

I agree with what Lilygloves just said. The whole quote "I'm going to live like a Narnian, even if there isn't any Narnia" is a bit of a mouthful for a movie tagline. Maybe they should shorten it to

"Live like a Narnian"

I can kind of see that at the end of the trailer, or the top of promotional posters etc. I like it.

hmmm, I'll take a crack at it

just when everything was going fine... (clip of green snake & intense music)
everything took a turn for the worst... (clip of jill saying "oh, bother the signs!")
The Chronicles Of Narnia: The Silver Chair (epic music) rated PG Coming to theters soon (we hope)

That was more like the teaser.... then a tag line...
Oh well...

^ Anhun gasps in horror as she envisions a "Sing-along with Jill" version of Silver Chair.

I just died laughing in my chair