Rattle Bones Pluto is a Premium Box Tsum. He is a Limited Time Event Tsum and is not available through purchasing Premium Boxes. Known as Honehone Pluto in the Japanese version. He was introduced to the International version in tandem with the Halloween 2016 Event (October 2016).
When your skill meter is nearly full, while you are going to make a long Pluto chain (or a chain with big Pluto), you can quickly activate skill after the long chain, so that the skill meter can be re-charged again (with most of the Pluto count from your previous long chain).