Mashed potatoes can be frozen, just think of all the Hungry Man Dinners out there in Freezerland, ha. (Didn't/don't they have mashed potatoes in them?) 😀
You could make up something like some Shepherd's Pies (with venison?) with mashed potatoes on top and then have an easy meal to cook later on, if you have enough room in your freezer(s).
I've frozen Cottage Pie before, but I can't remember if I browned the potato topping before freezing or not. I think either way will work, but you might want to allow it to thaw a bit before heating.
Here's an example of one not browned in advance, but thawed before final cook.
https://food.unl.edu/shepherds-pie-including-directions-freezing