Humanity, Chaos, and daemons.
All of them were frozen in time and space by the Tzeentch sorcerers. Only they could see Tzeentch's illusory projections constantly appearing, but they were merely phantom reflections.
"It's Gamma World!"
Very quickly, the Tzeentch sorcerers realized where these people had come from. Only Gamma World would employ warrior mechs with such absolute loyalty and faith in the machine spirit, along with previously unseen Power Armor and weapons.
These forces of Chaos had heard some news about Gamma World before, but only now, when they truly saw Gamma World, did they realize their understanding had been incomplete.
They had previously been astonished that certain Chaos factions feared such a tiny world, and had even thought nothing of Tzeentch's interest in it.
Only now did they understand how formidable Gamma World's military strength was and how ferocious its fighting could be. These soldiers might have had such immature flesh, but their souls were as resilient and incorruptible as if tempered over ten thousand years. Nearly every one of them possessed immense resistance to Chaos corruption.
Furthermore, their fighting methods and combat experience were so extensive that it felt unbelievably familiar to them, as though these people had begun learning how to fight Chaos in their mothers' wombs.
These battle-hardened warriors were hunting on Three Gates Star.
The soldiers of the Imperium watched these Expeditionary Forces pass by them and realized that they shared the same enemy. Over years of warfare, they had long developed the habit of coordinating with one another. Even without being told to cooperate, they could still work alongside the Expeditionary Forces and win battle after battle.
"District Nine has been cleared. Air-drop operations are underway in District Ten. Don't let a single Chaos force escape. Make those Nurgle and Tzeentch sorcerers disappear completely."