It's part of the promo set that comes with preorders for Wrath of the Cosmos. So if you preordered you'll get Knyfe along with the Prime Wardens when the container gets out of shipping hell.
Did you see someone posted a review for WotC? I'm wondering how the heck he got a copy before anyone else!?
As explained in that thread, some stores received copies of the expansion (without the extras):
You must have gotten in just before they were asked to pull it.
GtG received the container with the actual expansion boxes, and expected the container with the "extras" (mini-expansions, promo cards, art prints) to be not far behind. They therefore shipped it to some of their retail partners expecting to be able to package and ship things to pre-order customers within a day or two.
The second container got held up in the port strike, and was not in St Louis when last I knew. They've contacted the folks who got it early and asked them to pull it from the shelves.