I am stealing this idea from Marioboards, for I am nothing but a crook.
Basically one person adds something to the image and then someone else add another thing and it goes on until a new base image is made. Now go.
This thread is basically what it sounds like! You put in custom stages you've made in Ultimate and people get to marvel at them. You can also give help to other budding creators. ( Like me! )
Don't have any custom stages right now, but that'll soon change, I hope.