The first layer is one of the four cake layers. Put this on a cake tray, or whatever tray you will be keeping the entire cake on. It will be difficult to move once it is assembled.
Carefully, using an offset frosting spatula, put frosting on top of this cake. Then crush some Oreos, and add a layer on crushed Oreos on top. I would use about 1/2 of an Oreo sleeve for this. (The Oreos should be crushed, not whole. Otherwise the second cake layer will not stick on top if it does not touch the icing underneath).
Repeat the same as Layers 1 and 2
Repeat the same as Layers 1 and 2
Now put the last cake layer on top of the crushed Oreos.
This last frosting layer will be the top of the cake. Make a "crumb coat" over the cake. This is a layer of icing all over the top and sides of the cake, completely covering it in white frosting. This crumb coat prevents crumbs from coming into the real icing layer.
After the crumb coat, refrigerate the cake for an hour to let it set.
Now to add the real frosting layer on top of the crumb coat. Using the offset frosting spatula, put frosting to cover the entire cake.
Put crushed candycanes all along the outer bottom edge of the cake using your hands. You will have to press the candycanes into the frosting, as shown in the pictures of the cake above.
Refrigerate the cake for a half hour to let it set.
Using the chocolate topping in the squeeze bottle, cover the entire cake top in chocolate topping, and use a frosting spatula to spread it around. Then on the sides, "drip" the chocolate like it shows in the pictures above.
Using the piping bag with a star icing tip and red frosting within it, pipe icing (as shown in the pictures above) into 8 circles around the cake. Top with half an Oreo slice each.
Sprinkle some Christmas sprinkles into the middle of the cake.
Refrigerate the cake for about an hour to let it set, then serve!