The Emperor and Horus fighting across space and time

You make your riposte. The Himalazia. The roof of the world that was. A fierce blue sky and fiercer cold. He reels from this counter-attack, and you slide together down a steep slope of powder snow, exchanging blows at close quarters. You show Him you can fight as unscrupulously as Him. These are the soaring peaks that His pride will level. Let Him contemplate a lonely death here, unmourned and unmarked, surrounded by the snow-capped emblems of His titanic hubris.
He does not waver. He maintains His rate, not a hint of gapping in His guard, driving you down the blinding white flank of snow, ice crystals swirling around you like winter breath, His sword seeking your heart, His claws hunting your throat. You stop the blade with Worldbreaker's haft, lunge with your Talon–
He parries you with Isstvan V, still white-hot and smouldering from your victory. The air is dense with virus smog and organic ash, and the ground beneath your feet is a solid block of fused ceramite like a toppled frieze depicting battle-brothers at war. Perhaps He can illuminate you. How is this supposed to hurt? He did this, not you. This atrocity is His fault, and with your next blow, you show Him why–
Molech. Yes, Molech.

-Siege of Terra: The End And The Death - Volume three