Well, that was easy.
So, as for the Plot... Since it's a dream world which means we can have pretty much anything, the most prominent issue is therefore going to be why it's a dream world, and why pretty much anything is in it. I don't usually do dream worlds I'll admit, so this is a stab in the dark; I have no idea whether it's a good idea or not, but what if:
Someone had developed a piece of technology that allows you to go into people's dreams Inception style (although only allowed viewing, not editing), and marketed it as the next generation in entertainment - for £500, you could watch people's dreams. Before long, someone figured out how to store the dreams as data, and had made a living network out of the technology - sort of like an Internet 2.0, but where instead of sitting at a monitor, you actually go inside the network?
This would end up a kind of parallel Earth that replicates normal Earth in most ways (dreams are represented by buildings, for example, and to visit the dream you enter the building.) Think of it as similar to The Infosphere from Futurama, or that episode of Southpark where Stan gets sucked into Facebook, except instead of websites, you go there to experience dreams.
The plot would then revolve around a terrorist organisation that was using these dreams to wreak havoc on civilisation by drawing fantastical beasts and laws from random dreams.
Of course, I realise that this is more sci-fi than fantasy at this point, so if anyone has another idea that better sticks to the fantasy theme I'd welcome it.