The Emperor teleports an Ork reactor imbued with enough Orkish warp power to shake apart a planet

"Horus had no knowledge of the insane mechanics behind the greenskin power core, but any fool could see that it was spiralling to destruction. The powerful tremors shaking Gorro apart was evidence enough of that, but to see the bound starfire straining against its bonds was to know it for certain. Had the death of the Mech-Warlord been the final straw in breaking whatever bonds of belief held its monstrous power in check? How long would it be before it exploded? Horus had no idea, but suspected it would be long before any of them could escape the depths of the scrapworld.

‘This can’t be how it ends,’ whispered Horus.

‘No, my son,’ said his father, gathering the golden light within him once again. ‘It is not.’

The Emperor clenched his fists and the air around the seething plasma ball folded. It turned sickeningly inwards, as though reality was merely a backdrop against which the dramas of the galaxy were played out.

And where it folded, the spaces behind were horribly revealed, great abysses of crawling chaos and unlimited potential. Howling voids where the combined lives of this galaxy were but motes reflected in the cosmic dust storm. An empyrean realm of the never-born, where nightmares were birthed in the foetid womb of mortal lust. Things of void-cold form writhed in the darkness, like a million snakes of ebon glass coiled in endless, slithering knots.

Horus stared deep into the abyss, repulsed and fascinated by the secret workings of the universe. Even as he watched, the Emperor drew the fabric of the world together, sealing them around the greenskin plasma core. The effort was costing him dear, the golden light at his heart waning with every passing second.

And then it was done. A thunderous bang of air rushed to fill the void left by the plasma fire, and the backwash blew back into the chamber in a gale of sulphurous wind. The Emperor fell to one knee, his head bowed.

Horus was at his side a heartbeat later.

‘What did you do?’ said Horus, helping his father to his feet. The Emperor looked up, colour already returning to his wondrous features.

‘Sent the plasma core into the aether,’ said the Emperor, ‘but it will not last long. We must withdraw before the warp fold implodes and takes everything with it. The entire mass of this scrapworld will be soon crushed as surely as if it had fallen into the grip of a black hole.’

‘Then let’s get off this damn thing,’ said Horus."

-A Wolf of Ash And Fire