Bane of Empires
Tzeentchian daemons are the ones who Tzeentch would be most anxious to keep secrets/knowledge from. Outwitting the guardian and passing through the nine gates results in the aquisition of "infinite knowledge". That's the kind of thing Tzeentch doesn't want his daemons possessing. Unless of course at some point in his eternal scheming he wishes to contain and reduce his own power and influence.and since he is a tzeentch daemon anyway, he would probably have known the riddles answers easily.