Karin Shadestep is the Ninja: She is a practitioner of martial arts shrouded in utmost secrecy from the rest of Azeroth. She is but one of the many unseen heroes righting what is wrong, and making sure the order of the world as we know it is upheld.
For a development timeline of the Ninja, refer to the below spoiler:
The Basic Set provides the framework for this class, introducing the most core of mechanics, flavours, and playstyles. This set introduces weapons, a limited degree of tokens, powerful transformations, a faster playstyle in the form of continual chip damage, and value generation through copying your own cards..
The Grasshopper (Initiate) cards build up and outwards from the Basic Set. The Reprise keyword is first seen here, formalizing the Ninja's identity of copying their own cards in order to defeat their opponents. Kunais are also seen en masse in this set, adding onto the Ninja's class fantasy.
Like Demon Hunter, Ninja arrives in the middle of Hearthstone's history. Rise of Shadows is when Ninja drops, and they are on the side of the League of Explorers. They have determined that the League of E.V.I.L. are victorious based on future events and have sent operatives back in time to aid the Explorers! They bring with them powerful spell manipulation as well as a splash of Discover shenanigans.
Reprise is Ninja's class keyword. It is very straightforward and functions exactly like The Caverns Below where both copying and bouncing a minion back will meet their requirements. Ninjas place a very heavy emphasis on copying their own cards to achieve Reprise, though simply playing the other copy of a card in your deck will achieve the same result.
Note: Goya's Invoice was designed by Jengus. Markerlight is the "oddball tribe" Challenge card. Furthermore, The Transient Knife was a weapon as Jengus wanted a Legendary weapon. (Markerlight is the 40k reference, Mvon.)
Grasshopper (Initate) Set
A hearty thanks to all of the contestants and voters in the contest. While not without its faults, this contest was a success!