Is it okay to give a ferret unsalted mashed potatoes (made xtra creamy) as a very rare snack?

It's not going to kill him, if that's what you mean. Ferrets are renowned for being lactose-intolerant (though I don't think that applies to every ferret). A lick now and then, in my opinion, is fine. Just remember ferret really have no need of starches/carbs or dairy. Their bodies don't use the nutrients (lack a cecum that is essential to getting nutrients of veg/fruits). I'm sure you're going to hear a lot of differing answers. Just remember: not needed but not fatal or illness-inducing at a lick or two/week. Hope this helps!

The little bit he did get shouldn't cause any major problems (keep an eye on him just in case though), but I wouldn't willingly give them potatoes on a regular basis. Ferrets are prone to pancreatic problems (insulinoma) and potatoes are pretty high on the glycemic index, which can, in high amounts, cause (or, at least, help lead to) some of those pancreatic problems. Like I said, the little bit he did get shouldn't cause any harm, but never willingly give him any potatoes.

I don't think it will hurt if it on occasion,I have 2 ferrets and I can not eat a bowl of cereal without one of them crawling up my arm and almost doing a nose dive in my bowl, she loves to drink the milk out of the bowl while I am trying to eat.Just watch her poo to make sure she is not getting diarrhea.Happy eating with your furry friend.

Try it and watch his poo. If he gets diarrhea or he is constipated, don't give it to him..Otherwise, let him enjoy! =)