Out of the 4 ruinous powers, one could say Tzeentch is the scariest to be possessed by.
Khornes possession is like giving in to the red mist and venting out your rage for eternity.
Slaaneshs possession is like a high with bouts of clarity before falling into another high until all you can do a seek an even greater height.
Nurgle is like being overcome by anxiety and depression until you forget it and continue on as a husk.
But Tzeentch is different because you don even know it until your usefulness is up. Using your own arrogance against you, you believe your actions are of your own accord. Even if you find out, you believe its only for a moment as all are a part of his great plan. In the end, its only once you are no longer of use that you know you were a mere toy to the outer God of change/hope.
In the maze of perpetual change, a familiar figure walked around perfectly, navigating the realm of Tzeentch. His appearance changed, and he looked exactly like Odin except for minor differences. His hair was White and reached down to his hip. His eyes were heterochromatic, having scarlet red and grey eyes.
Playing with strands of his perfect hair, the guardian looked around and took control of the realm, bending it to his desired will. To the guardian, this entire universe was nothing but a mere game, actually, that was too high of an appraisal. This world was more like that boring idle game you would play when you had nothing else to do.
Tzeentch was nothing to the guardian. He had met stronger literal ants than Tzeentch one had even eaten a quarter of reality, which held around 72^100^100^100^100^1,000multiverses. He made his way towards the weaver of fate and made his introduction to the terrified Chaos God.