Horseman of Death
Just like the Slaanesh Knight, I had to think about why Tzeentch would be the Knight of Death. If final hit on me that as the model will have a strong Egyptian look to it and that ancient culture had a strong cult of the dead, it all fits just fine.
Looking around Pinterest and the web I found few Tzeentch based knights. Most were going in the same direction as I was moving with a strong Egyptian look, but a few had also added in some astronomy bits.
Looking through GW’s model kits I found the Celestial Hurricanum which offered all kinds of great stuff to add to the model. I also might add the torches from the Excorist kit and a few bits here and there.
I also got my hands on the greater deamon of Tzeentch for added bits. I might swap out some of the planets from the Celestial Hurricanum kit with bits from the deamon kit.