Before there were creepy clowns, there was Jasper, the creepy court jester. A social outcast, Jasper found himself gravitating to the boss after he promised Jasper all the friends he could ever imagine. In exchange for Jasper's scare intimidation tactics, the boss will grant him access to "Bookface," a dark gift given to the boss by the Dark Alchemist.
Each mastery level adds another card to the cardpool for defeating Jasper. Each of the bronze, silver, and gold mastery levels unlocks a new card, while it takes all three diamond and onyx levels to unlock a single card.