Process sugar and butter in a food processor until very creamy, scraping sides as needed, 1 to 2 minutes. Add the eggs and yolks, one at a time, pulsing after each addition. Add the milk, water, and vanilla and process to blend.
Whisk both flours, baking powder, and salt in a medium bowl. Add the dry ingredients, in 3 batches to the wet, pulsing, and then scraping batter off the sides of the processor as needed after each addition. Process until the batter is very smooth and pourable like pancake batter, about 2 minutes.
Evenly pour the batter into the prepared cups, filling them 3/4 of the way full. Bake until the cakes are just firm and spring back when gently pressed, and the tops are golden, 18 to 25 minutes. Cool slightly in tin, and turn out of tin when cool enough to handle. Cool cupcakes completely on a rack before frosting.
For the frosting, whisk the milk and vanilla extract together in a small bowl.
Slowly beat the butter and sugar, in another medium bowl, with an electric mixer until incorporated. Raise the speed to high and mix until light and fluffy, about 5 to 7 minutes. (Occasionally turn the mixer off, and scrape the sides of the bowl down with a rubber spatula.) Add the fluff and salt and reduce the speed to low. Add the milk and vanilla mixture, scrape the bowl down, and mix until fully incorporated. Raise the mixer to high and beat briefly until fluffy, about 1 to 2 minutes. Use immediately.
To decorate, frost the cupcakes.
Top each cupcake with a snowball cake. Pinch the marshmallows slightly to make bunny shaped ears and spread them with some frosting. Dip them into shredded coconut. Insert a pretzel stick carefully into the marshmallows and insert them into the snow ball to make bunny ears.
Dot the back of the candy eyes with frosting and press them onto the snow ball below the ears. Frost the back of the jelly bean and place below eyes for the nose. Frost the tip of the mini marshmallows and place them around the nose to make nose pads and buck teeth. Place the liquorice dot just above the teeth. Dip the straws in frosting and place under the nose to make whiskers.