Proposed Canon
Hat Magic is one of the three disciplines of the Magic class Stagemancy; it is aligned with the axis of Erf and composed of all three elements of Life, Motion and Matter. Erf-b1-p038a It was used, along with Thinkamancy and Date-a-mancy to create Duncan Scone's Laurel of Napster.
Hat Magicians appear to have a job finding network similar to the thinkamancers. Instead of being able to send out a general call however, Hat Magicians must use message hats and job posting boards. This is slower, but cheaper.
- Creation of Magic Hats.
- Message hats can be used to send small items, like written messages and gems. These can be used by non-casters. It is unknown whether message hats are linked to one another, or whether they can be used to send items to any unit who has a message hat.
- Thinking caps can protect against being fooled and counfounded.
- In the hands of a Hat Magician, a Magic Hat has been used for small object conjuration.
- Pulling rabbits out of hats to attack the caster's enemies. Cubbins uses this to "Pop a Cap" (the page picture above).
- Creation of snow golems, which is completed by putting a hat on the snowman's head.
 Known Hat Mages
As the traditional use of pulling thing from a hat hints at, Hat Magic is linked to instantanous transport such as portals and could include some type of hammerspace as a natural form of it.
This hints that the possibility of using hat magic to conceal your gems in portals attached to terrain features - hidden trapdoors, if you will. Anything involving (for instance) three obelisks which will open a hidden area if you put a ruby on each and say the magic word "Avalon", would be hat magic. The portal that got the casters out of Gobwin Knob before the volcano erupted would have been hat magic.
Hat Magicians are sometimes referred to by the title of 'Haberdasher.' Most female Hat Magicians go by this title as well, though they may go by the title of 'Millener' if they specialize in making hats for female units.
Hat Magicians can carry a stack of Orlies in their hats, extending their range as scouts, similar to a Transylvito vampire carrying Doombats in his coat. Alternatively, a Hat Magician may carry Killer Rabbits in their hats. However, Hat Magicians cannot carry Orlies and Killer Rabbits in the same hat; it must be one or the other.