I admire your imagination, Charles. A great deal of Pokemon with unordinary features, almost too many. I mean, roughly estimated over 50% of them have traits we'd call 'Legendary', while in Pokemon games, only a minority of a Region's Pokemon would really fall into the 'Legendary' category. Mentioning biblical things like The Garden of Eden and Leviathan from the Book of Job aren't what I initially expected to appear in Starter Pokemon and their evolution's PokeDex entries. But on the other land, this makes your Marshiso Region more exciting, at least. So no real disappointment there.

About the biodiversity, I see no issue in fitting any of your Fakemon into the Region based on Michigan. Also in the real Pokemon games, we see plenty of artistic freedom in placing different Pokemon placing into their respective environments. Take Ruby, Sapphire and Emerald for example. Although Kyūshū is more of a tropical environment we still see Ice Pokemon there. There's more, I have always found it odd having Route 111 Desert there, because there isn't really such terrain in real Japan (except Tottori sand dunes).

Only a few typos. Mostly stands out that you referred to your Region as 'Mashiso' in one point and 'Marshiso' in other. As I'm not a native English speaker, my grammar isn't so good, so I really can't judge you there.

What I really can nitpick there, is my favourite one of the Fakemon you presented. It is, of course, Käärmeöljy. 'Käärme' being Finnish for snake and 'öljy' for oil. 'Kyy' or 'kyykäärme' is an exact counterpart for viper. Also, the word order does make a difference. Käärmeöljy sounds, to me, 'oil made of snake', whereas Öljykäärme would mean 'snake of oil'. English uses here a word order that is an opposite of the Finnish one, so I can't be sure which one you meant.

But all in all, very interesting writing!