in the Events forum there is a topic all about the Mazes. If you go back just a bit, you will find a list of horses needed to pass the obstacles. Its always a good idea to check the Events forum for a topic on a current Event as you will find any info you need there (or you can ask there). Its not really a question for a permanent FAQ because it will be obsolete as soon as the Event is over.
edited to add: Any coat from the Bewitched Pumpkin series will do, I just got through with a skeleton coat.