I did one for dd3 this year. Started with a rectangular cake (tray bake size) and some smaller round cakes and then built up the layers to make a body, head and face. I used marshmallows with those chocolate buttons with spinkles for the tail.
One thing I did do wrong was to put the butter cream directly onto the cake. I sued a chocolate cake that goes a bit crumby and it got a bit messy with crumbs in the icing. I just said they were splashes of mud and dd was happy!
If you use buttercream, to stop getting crumbs in it, do a thin layer of buttercream, don't worry about crumbs, put cake in fridge to set buttercream and then do the final layer over the top and then you won't get crumbs showing through.
If you cook a cake in a pudding bowl that would make the body shape, then all you have to do is cover that in pink icing and make face, feet and tails from fondant icing (colour with pink paste food colouring) and stick them on.
Bumpy becky yours is fab btw.
I've also made a Peppa pig cake before, covered madeira in green fondant, added icing flowers and made a 'muddy puddle' from melted chocolate and stood dd's PPig plastic charracters up in the puddle before it set.