Well characters around Mario's size would stand around up to Plessie's waste. And I used the artwork of Yoob & Yoshi as well to determine how big Yoob is. Yoshi stands up to Yoob's waste as it seems that Plessie & Yoob would be the same size. With Yoshi up to both Plessie & Yoob's leg I decided to have Ploob be that size where Yoob & Pless would be up to his leg/waist.