@Background Pony #89C0  
Actually i think this artist wrote a fic where he tested a fluffies internal body temp, It was 90 degrees, and he claimed if it drops by 5 it will die. So maybe that? However you are right, seeing as fluffies are also warm blooded. As for the human thing, i would say we look to closely at the little things and too often miss the big picture.

@Dangerous Amoeba  
I have no idea. I tend to post stupid things when I’m tired.
 
That being said, I’m sure this is horribly thought out when considering biology.
 
 
First of all, it would have to be FREEZING or BOILING water. Any water wouldn’t do. You wouldn’t get enough of a temperature difference by just using water from a tap. If you were able to kill a fluffy via thermal shock using regular water, it’s more likely that moving a fluffy from an air-conditioned room to outside would kill it.
 
If the artist isn’t referencing death by a type of thermal shock, but instead hypothermia that makes even less sense as, again, you wouldn’t get that kind of temperature drop with just tap water. Not only would it have to be freezing, but you would either have to keep dunking it in freezing water to drop the body temperature enough or be doing it in a cold environment. If you were to keep dunking it then drowning would be a more likely COD. In the case of a cold environment creeping, painful hypothermia and frostbite would most likely set in after a long run through the snow.
 
Here’s the better scenario:
 
Fluffy runs from some danger; snow gets caught in fluff; snow melts into water; transfer of heat in fluff becomes higher; fluff loses heat insulating properties; fluffy can’t feel legs; fluffy can’t feel everything; fluffy collapses; fluffy freezes to death, alone and unloved in the white, uncaring wilderness; fluffy is covered by the falling snow, leaving no traces as if the damned thing never existed.
 
See? More interesting.
 
If you are really sick in the head, you can make it double as an allegory for humanity and how while we are so caught up in solving immediate day to day problems we might miss smaller problems that seem like nothing but, after time, would accumulate and wipe us all out and, after time, would result in all we created crumbling into nothingness as if we never existed at all.

@Background Pony #89C0  
What does thermodynamics have to do with this? The fluff cools down, and its somehow enough to kill them.

Poor fluffy.

Downvoting because fluffy pony didn’t drown.
 
Also, thermodynamics doesn’t work like that.