Just like all the other challenges, hints can be used. Press for hints in the Challenges menu. This challenge only has to be completed once. At the end of the challenge there is a game of Rock, Paper, Scissors. Now hopefully you'll know how this game works, if not, it works like this:
The Baron will have a glow round him, whatever he is. Example, if he's paper, you hop into a Scissor doll just before he comes to get you, attack him, then attack him again when he is a smaller doll, then one more time and that's it done. If he gets into one of the Scissor, Paper or Rock dolls again, you will have to do it over again, he gets quicker as he gets smaller, using the inside circle to catch him works.