I made this Homemade Butterfly Tier Birthday Cake for my youngest son's birthday. I wanted this cake to be round but did not want to buy new cake pans. So, I adapted it to be square-ish. I wanted it more symmetrical but I ultimately liked how it turned out.
It is a basic marble cake with vanilla buttercream. I used a local cake shop's marshmallow fondant. All appliques and food items are marzipan colored with gel food coloring (this was the time consuming part). The colored balls are bubble gum. I had several problems with the plastic dowels that I used, this was my first time using them. I assembled the cakes and covered it all with one big piece of fondant, which was a mistake. I probably should have covered them separately, since my cake settled and the dowels poked through my marzipan butterfly. I had to pull them out with a pair of pliers, which affected the butterfly, but I think the bumps were less attractive. It went over really well and I mourned a little in discarding the uneaten portions.
I have used fondant for similar (although less elaborate) cakes in the past, but found the marzipan super easy to work with (as long as you keep your hands cold and clean with frequent hand washing and let the pieces cool down after working with them). They held up better than fondant, with less cracking and stuck to the cake well with a tooth pick to add support to the buttercream glue.
This was a pretty time intensive cake, which is probably why I only make two per year (one for each of my boys). Hope this gives some inspiration; I am totally a beginner and have had no formal instruction on what to do for cake decorating.