Pipe some cream on a cake and stack. Each time, pipe some cream before stacking. Cover the whole cake with buttercream. Insert two big skewers on cakes for extra strengtheners. So you would have middle dowel plus two big skewers.
Roll flat a yellow fondant, about 18 inch in size (I use The Mat to roll my fondant and it has measurement, so 18 inch on all sides. This is enough to cover my overall cake, sides and front), and cover your cake.
You can either stack the cakes right away onto the OSB body (pushing through the dowel) or you can cover the cake first then lift it up and push it onto the dowel. Whichever you find it to be easier.
Roll more yellow fondant, enough to cover the back of Spongebob.
Start decorating as Spongebob (make indents for the sponge with ball tool or even spoon)
Roll flat white fondant and cut into two rounds for eyes, red fondant for mouth, pink fondant for tongue. Cut white fondant into small strips for teeth, blue fondant for eyes, black fondant for lashes, etc.
Now to make the hands (which later my 7 yo protested why Spongebob only has 3 fingers, I honestly didn't know that he had 5 fingers like humans do hahaha). Roll two white fondants and two yellow ropes. Attach white and yellow with skewer and flatten the end of the yellow and shape into fingers.
For the nose, shape a yellow fondant into a somewhat rope and insert skewer.
Glue all fondant for eyes etc with a dab of water. While for hands and nose, push in the skewers into the cake
Voila, your stand-up Spongebob cake is done ^_^
Oh don't forget for the pants area, either paint white fondant with brown food color or attach premade brown fondant. And also make red tie :)