Preheat oven to 325 degrees F. Lightly grease two 6-count donut pans and set aside.
In a small saucepan over high heat, bring cider to a boil. Reduce heat to medium-low and simmer until reduced to 1/4 cup, about 15 minutes.
In a large bowl, whisk together the vegetable oil, applesauce, sugar, eggs and vanilla. Add the reduced cider and stir to combine.
In a medium bowl, whisk together flour, cinnamon, baking powder and salt. Add dry ingredients to the wet mixture and stir until just incorporated.
Transfer batter to a disposable piping bag. Pipe batter into donut pans, filling each well nearly to the rim. Bake until a toothpick inserted into a donut comes out clean, 12-14 minutes. Allow doughnuts to cool in pans for 10 minutes, then remove to a wire cooling rack and allow to cool completely.
Meanwhile, in a large bowl whisk together powdered sugar and apple cider. Tint to desired shade of green using gel paste food coloring (glaze should be the consistency of glue; thin with additional cider if necessary). Carefully dip the top of each doughnut into the glaze and decorate as desired with sprinkles, disco dust, a candy stem and candy leaves.