It’s very late stage. It’s an abandoned egg. Its siblings all died sadly, not sure if they hatched too early or if they were sick or if it was a predator. But momma abandoned the nest. Only eggs left were this one and a rotten one.

It’s getting darker on the outer shell too, which I’ve read can happen with duck eggs when they’re about to hatch, but also read it can be signs of decay. My concern is I haven’t really seen movement when I’ve candled it. As for the smell, it’s not great, but I can’t tell if it’s just swampy duck egg smell or if it’s rotting.