Combine marshmallows and butter in a large microwavable bowl. Cook for 60 seconds. Stir and continue cooking at 20 second increments until melted and smooth.
Add all remaining ingredients and stir until well combined. Place on a large parchment covered pan and using buttered hands, press until about 1" thick. The actual size of the rectangle doesn't matter.
Cool completely. Once cooled, cut out using an egg or oval cookie cutter.
Melt candy melts according to package directions and place in a sandwich bag. Snip off 1 corner and adhere SweeTARTS Soft Bites Bunnies and SweeTARTS Sour Bunny Gummies.