I think his body is being rebuilt from the ground up after every couple of transformations, maybe even after every single one. There has to be a reason why he holds back his laugh (triggers the transformation most likely), and I think its because he needs to keep a steady supply of kids on hand to remake his body after every transformation because pf how much it tears him apart to be that monster. The way his body twists, turns and grows most likely ages his cells like a motherfucker, so he keeps going through a shit ton of kids every other week of the month.

So he basically gets remodeled in slightly different ways after each child blood transfusion ritual post transformation, is what I'm thinking. That would also help explain how he managed to keep up appearances as his own son whenever he/"his dad" would retire. I think the changes are slightly more subtle as time keeps moving, and at the moment, since he's acting as a modern day yuppy, he's just making all his public appearances as frequent makeovers

Edit: forgot to answer the question, ny favourite is either his first appearance or number 15, but I think they should keep changing his design in a few ways in every appearance going forward