Halloween duck reskins:

[Apollo]

Here are the ones I've found so far. (will edit when more are found)

Yellow Duck: Has been changed to look like a vampire.
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Duck You! Duck: The words on it have been changed from Duck You! to Booh! (with an H for some.. reason?)
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Kiss Duck: Has been changed to have the word Q̸̮͓̓U̸̞̐̍A̸͈͕͍͆C̸̛̜̉͠ͅḰ̷̙ scribbled on it messily.
It's Quack has also been changed from the guitar riff to a death metal screech (though this may be permanent?)
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Skeleton Duck: Now carries a scythe.
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Wooden Duck: Now has nails in it.
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Daisy Duck: The main color of the duck has been changed from a light blue to a dark black.
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Glowing Duck: Now has dark around the eyes as well as some lines under them and a red circle inside of a black on on the beak.
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Stone Duck: Is now a grave.
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Gravel Duck: Is also now a grave.
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Day of the dead Duck: Has a bug on its head.
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Black Duck: Now wears a spooky mask.
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Knife Duck: The knife is now through its head.
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[KF4UYC]

Not a 'duck reskin' per se, but the golf ball usually found in the bottom of the pool is now an eye-ball. So, which ever one of you lost it please describe it to get it back...it creeps me out just laying there in the bottom of the pool looking at me!

[lightwo]

Don't forget the

Q̸̮͓̓U̸̞̐̍A̸͈͕͍͆C̸̛̜̉͠ͅḰ̷̙

https://steamcommunity.com/sharedfiles/filedetails/?id=3060143309

[A Tired Lesbian]

The rock duck that sinks to the bottom have different gravestones! I've only found 2 so far.
One of the Halloween ducks have a special quack that I've seen so far

[TenFootBunny]

Does the skeleton duck usually carry a scythe? I can't remember if that was part of its original design or an event reskin.

https://steamcommunity.com/sharedfiles/filedetails/?id=3060301995

[frostynostalgia]

Golf ball is an eyeball too.
Edit: Missed the earlier post

[frostynostalgia]

Wood duck has nails in it

[TenFootBunny]

Oh no... the wooden duck got hammered!

https://steamcommunity.com/sharedfiles/filedetails/?id=3060308556

Edit - looks like I crossposted with frostynostaglia up there. ;)

[frostynostalgia]

Knife duck has the knife through its head

[frostynostalgia]

Black duck has a mask

[TenFootBunny]

The glow-in-the-duck put some glam in its glow
https://steamcommunity.com/sharedfiles/filedetails/?id=3060319937

From the depths...
https://steamcommunity.com/sharedfiles/filedetails/?id=3060328089

[frostynostalgia]

I really want to scan the ghost duck.

[frostynostalgia]

Day of the dead duck has a bug on top of it