I have to ask the why question. Why are these creatures existing? Where did they come from? Ecology? What nitch do they fit into? What will you not find in a swamp that has Marshwiggles in it?
I would add a disadvantage for being too dry. You have a good deal going on there for a mere 1 level adjustment. Say a -1 to all rolls if their skin is not kept moist. You do seem to have a frog thing going one here.
I disagree with the high wisdom statement if they are constantly bathing in doom and gloom. Someone that is wise will have perspective. The Marshwiggles seem to lack that. I would drop the wisdom adjustment. You might have to appear wise with the melancholy demeanor and slow steady speech habits.