A suggestion if anyone needs a Great Beast in the France region - The Peluda.
With some creative interpretation of the legendary tales, it probably started off as a tortoise heart-beast, that followed the Inner Mystery of the Chimera and now is part hedgehog/porcupine. Green might be explained as being still for long enough periods that moss grows on it.
I think the Normandy or Provencal Tribunals have something like it, but as a Magic Creature.
One of the books I don't have
Any other mythokogical mentions that could be interpreted as a Bjornaer Great Beast?
Considering the number of shell-backed dragon-like monsters in stories, there must have been some dangerous tortoise-turtle-terrapins crawling around Europe in the Very Old Days.