What is This Used For "Splinter of Darkness"

[fastjaw24]

I got a Magic Recipe for Splinter of Darkness and created one only to find out that pretty much all stats are for the undead in your army.

+10 attack of Black Knights
Black Knights always counter attack
No Ghosts/Cursed Ghost on the battlefield can increase their numbers higher than their starting amount

As far as I know I am getting close to being finished with the game I have only 2 islands at the bottom of the map unexplored and I have not seen any undead units for sale. Which they are the main antagonist for this game so I am guessing that is why you can not use them like previous games. So is this just another stupid item that they forgot to take out of their beta game before release or is this actually used in the future on a quest?

Thanks for any insight someone can give on this