The cake is chocolate with a cream cheese filling and frosting. The entire cake is covered in butter cream fondant. Each tier is angled to give the unique angles.
All the detail elements are made from fondant as well and the Monster Truck topper is an actual toy truck. The mud is cream cheese frosting covered in Oreo crumbles.
Topsy Turvy cakes are a little more difficult to assemble than regular tiered cakes. They are stacked the way a flat tier is assembled, but if the angles are cut too steep the top tier(s) can slide right off. Structure is very important when making these cakes.