If you are writing for a tabletop army or fan fiction, these fit the "Chaos Space Marine" aesthetic:
In a world of shadows, the only weapon against darkness is the legion of demons you command. Chaos Legion
"The warp is limitless power and its secrets are infinite... It takes only the discipline and the will to shape it; those who lack that clarity of purpose are liable to be shaped by it instead." Legion Battle Cries: If you are writing for a tabletop army
“The Word Bearers are the best for showing Chaos as a fanatical religion, pulling from the full arsenal of mutants, cultists, and the Dark Mechanicum.” Reddit · r/40kLore · 2 years ago Chaos Legion
If you need flavor text or a tagline for the PlayStation 2 classic, these draw on its gothic themes and the summoning mechanics: