Combine water, sugar, and salt in large bowl, and sprinkle yeast on topo. Let sit for 5 minutes or until mixture begins to foam.
Add the flour and butter, and mix on low speed until wee combined. Add a ½ cup of rainbow sprinkles. Mix on medium speed for about 4-5 minutes until dough is smooth and pulls away from the side of the bowl. Remove dough from bowl.
Clean the bowl and spray with oil. Return dough to bowl and cover with a tea towel, and let it sit in a warm place for about 50-55 minutes, or until the dough as doubled in size.
Preheat oven to 450ºF. Line baking sheet with parchment paper and spray with oil.
Bring a medium pot of water and the baking soda to a rolling boil. Turn dough out onto a slightly oiled surface and divide into 16 equal pieces. Roll out each piece into a 12-inch rope. Loop a dough rope to form a circle in the middle, but with about 2 inches of dough on the ends. Roll the dough ends into coils on top of the circle to form a Mickey shape. Place onto prepared baking sheet. Repeat for remaining pieces.
Use tongs to place pretzels into boiling water, one by one, for 15 seconds. Removed form water and place onto lined pan. Brush tops of pretzels with beaten egg and sprinkle with more rainbow sprinkles and sugar.
Bake until dark golden brown, about 10-13 minutes.
Transfer to cooling rack for 5 minutes before serving.