Carnymancy is one of the three disciplines of the Magic class Stagemancy; it is aligned with the axis of Fate.Erf-b1-p038a
Carnymancy is described by an apparent carnamancer as a magic to fight Fate and [succeed], or in the words of Parson validated by an apparent carnamancer, "the magic of rigging the game." 
It may be the way to defeat other magic, as Jojo claims that he has a spell that can send Parson back to Stupidworld.
As indicated by the Predictamancer, Marie Lavare, like a Carnival Carny it may be Canrymancers take non-carnies as stooges or suckers to be played, that is as pawns, and hence lied to as required to get Fate to play out as they will. After all who, but a master cheat, would claim to be able to cheat Fate itself.
Jeftichew, aka Jojo, formerly in service to Unaroyal, now residing in the Magic Kingdom. First Intermission 43
- Possibly the Fate magic behind the Arkenhammer.
- May reduce enemy abilities, similar to how carnival games are 'fixed' to be disproportionately difficult.
- May have minor abilities of other schools, which would explain why the Arkenhammer has so many different and wild abilities.
- May involve taming of wild units, which would correspond to the Arkenhammer, like in a circus carnival.
- May involve mesmerizing the enemy with flashy production values, if Carnymancy was the extra element in the Vanna "Wheel of Fortune" linked Turnamancy spell. Since carnivals involve fooling the "townies", are there links to Foolamancy?
- Being in the Fate axis, could involve the alteration of cause and effect, totally redefining the show.