This is what I have so far, the larger part will layer over sonic to give it some depth, think of it like the ridges on a lilly pad:
Of course if you don't want a ridge, you don't have to use it.
the thin part will be what he stands on, I made a variation with a flower on it for some variety. Obviously he won't collide with the flower.
The vine is going to be extremely difficult to make, as I'm not sure how you were planning to simulate the gravity with it, I'll need more details before I can do anything about that.
Seaweed is surprisingly hard to do...