One similarity between the Grey Knights and the forces of Tzeentch in 40k are that both are strong in pyschic power. In this preview, we get a look at some new powers they'll be getting in their new codices, coming to pre-order this weekend.
From the article:
With the Hexfire battlebox coming up for pre-order this weekend, alongside new codexes for both the Thousand Sons and the Grey Knights, we couldn’t wait to tell you about some of our favourite new psychic powers. Both of these armies claim to possess the strongest Psykers in the 41st Millennium, and they can’t both be right. So let’s take a look.