At first, I thought he was the one dropping the pops all over but once we found out it was the Tooth Faerie Baron that theory held no water. After the final dialogue, I then just figured that he must be the Candymaker's Ghost that all the 'spooky' stories in the Glimmerwoods were about.... but the back of his card calls him Harold the Headless Horseman as though we're meant to know who Harold is! So all of this is to say that none of my theories panned out in the end and I've no idea who it is!
Sadly, there are no drops because the Headless Horseman is merely a walker.