Mix the cake mix, lemonade, greek yogurt, and eggs on low speed for 30 seconds, then medium speed for 2 minutes. Fill cupcake liners 2/3 full and bake for 20 minutes. Remove from muffin tins to let cool on wire racks.
For the Frosting:
Beat the butter until light and fluffy, add the marshmallow fluff, vanilla, 2 tbsp of lemonade and lemon zest. Beat until fully incorporated, scraping sides of bowl when needed. Gradually add the powdered sugar, again scraping sides of bowl when needed. Add more lemonade if you desire the frosting to be thinner consistency.
To Assemble:
Drop 1/2 tsp of lemon curd on top of each cooled cupcake, pipe the frosting around the lemon curd and swirl on top to cover. Decorate with yellow sprinkles or extra lemon zest if desired. Enjoy!