I made this cake...
It's covered in BC and the decorations are MMF. They started sliding down the side and I think the only reason they didn't keep going was because the piping on the bottom stopped them. They are a little on the thick side. Could that be why--too heavy? Should I have used something to attach them (I just stuck them on)?
They were probably too heavy for just the buttercream to support them. I usually put a dollop of buttercream on the back to help glue it on. If they are really heavy. I stick a toothpick in the back (not poking through the fondant) of the decoration and stick the toothpick into the cake. If you do that, make sure you tell them.
Thanks for the toothpick tip!