Muscovy with gray caruncles

[Muscovynmore]

One of my drakes stopped moving and eating today. He's very light (down to <five pounds), but more puzzling is that his caruncles have turned from red to dark gray and wrinkled. It's been very warm here, so I don't think it's frostbite. I think I heard something about oxygen deprivation once, but I can't find any link to caruncles online. Can anyone help?
I don't have much hope for him because he's barely moving, but I can't help him without something to go off of. . . .

 

[Eggcessive]

I'm sorry that I don't know anything about ducks, but after doing a little research it says they can turn black from trauma, abscesses, frostbite, and I was wondering about maybe a fungus infection? Do ducks get favus like chickens get?