I was inspired when I saw the Tinkerbell cakes on this site! This was my first time using fondant on a cake (and only my 2nd cake ever) and it was much easier than I anticipated. To figure out how to do some of the basic work ahead of time, youtube was very helpful!
For the Tinkerbell cake, I just used a mix, but needed 1 1/2 mixes to fill the Wilton Classic Wonder Mold. The other half of the 2nd mix I used to make a small round cake for my daughter to enjoy all to herself.
After letting the cake cool completely, I frosted the entire thing with buttercream frosting. Then I used the leaf green Wilton concentrated coloring to work into the fondant, just a little bit at a time. I used powdered sugar to keep the fondant from becoming too sticky when I started to roll it out.
To make pleats in the skirt, I pulled small chunks from the fondant and rolled them in my hands to make a shape like a cigar that tapers at one end. I placed about six of those evenly around the skirt on top of the buttercream.
For the skirt, I started with the fondant in a cylindrical shape, and rolled it out into a long rectangle, only about 1/4 inch thick. To transfer it onto the cake, I draped the whole thing over the rolling pin and then guided it into place over the cake, lightly pressing it into the buttercream to hold it in place.
As someone else suggested, I wrapped the Tinkerbell doll in plastic wrap from the waist down before putting her into the cake. Once the fondant was on the skirt part, I put the doll into the cake (if she was any taller, I would to have had another layer of cake on the bottom). To make the bottice, I just used a paring knife to cut the fondant into the shape I wanted and then used royal icing to help stick it in place on the doll.
I then added a bit more color to the fondant to make a deeper green and cut the leaves for the skirt and the ribbon for the bottom out of those, using the royal icing to stick everything in place. Then, I used buttercream that I colored purple to go around the waist and the bottom of the skirt (hiding any uneven edges or mistakes). Lastly, I used some leaf green sparkle dust that wilton makes to add a shimmer to the whole thing.
For the small cake for my daughter, I used leftover fondant to make the #2 and to create a band around the cake, but left most of it buttercream so that she could dig in and enjoy - and enjoy she did!