Continue on with the supportive care, and hopefully, you'll keep seeing improvements.
I'm interested to see the video of him, and pictures of his droppings. Green droppings often indicative of an anorexic state.
Could you post a video of the duck?
Do you have any pictures of his droppings?
Where are you located in the world?
Several conditions can cause a sudden onset in paralysis with waterfowl, ranging from toxicosis, bacterial infections, trauma, to neurological damage. Differentiating these...