If one shakes hands with a Spriggan, intentionally or not, it creates a binding deal and the person must complete a favor for the spriggan. If one attempts to escape a deal made with a spriggan, he literally reappears in front of them.
Balzac was a Spriggan.
Spriggans are legendary creatures known from Cornish faery lore. Spriggans were depicted as grotesquely ugly, and were said to be found at old ruins and barrows guarding buried treasure and generally acting as fairy bodyguards. They were also said to be busy thieves. Though usually small, they had the ability to swell to enormous size (they were sometimes speculated to be the ghosts of the old giants).