As part of our pre-production we've been producing concept art including character and background designs to match the ideas.
My initial character designs - trying out various shapes and armour/weaponary ideas (use of bottle caps as shields). Plus a rendered version for fun.
Concept design. I figured that the elements could all pop up like wooden scenery (the clouds are held up by strings), complete with a frame, whilst myths and legends are told.
The northern lights could be a beautiful part of the scenery. This design style might be too 'grown-up' for the target audience though.
A younger style. It'd be pretty cool if the mice lived in a viking helmet.
Concept art for location. Again, possibly too 'grown up' but perhaps elements of this style could be used in a more toned-down way (especially the clouds).