Here are a few ideas:
Potato patties:
About 1-1 1/2 c leftover mashed potatoes
1 egg
3 T. flour
Mix all together.Fry about 4 min on each side till brown.

My Favorite Rustlers pie
2 c mashed potatoes
4c shredded cabbage
1 chopped onion
2t minced garlic
3/4t dried thyme
2 lbs ground beef
1 16oz crushed tomatoes
1/4 c dry red wine(optional)
2 T all purpose flour
1/4 c parmesan cheese
Add 2T butter to pan saute cabbage until soft. In another pan cook onions and
ground beef until done. Add garlic and thyme.Add tomatoes, wine, flour salt and
pepper. Cook about 4 min until it starts to thicken. Transfer beef mixture to
a 3 qt dish. Smooth out. Fold cabbage into mashed potatoes. Spread over. Sprinkle parmesan cheese over that. Dot with butter.Bake at 400 degrees uncovered for 35 min or until potatoes are golden.
Hope you enjoy this. My family really does.