Even out the circle cakes with a knife, then sandwich them together with butter cream icing.
Using lots of fondant icing mark out the shape of yoda's face, if it doesn't stick to the cake use some water.
Cut out ear shapes out of the rectangle sponge and use icing to make the dimensions of the ear.
Dye the icing green (leave a bit of white for the eyes) then roll it out and smoothly cover the ears and face.
Add a slit and extra icing for the mouth shape, roll out and shape some white icing for the eyes and add a blob of chocolate frosting for the centre. Using a knife cut wrinkles, but not too deep :)