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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.
You either need the Christmas Ghost Divine, a horse with the Ghost Bewitched Pumpkin coat or a horse with a ghost companion to pass the ghosts in the mazes event.