The Battle of the Cowl Crucible was a surreal skirmish between the Galactic Empire and a group of miners in the vicinity of the Cowl Crucible. As the Galactic Empire navy led by Darth Vader went into the depths of the crucible to retrieve cortosis, the local Rebels opened fire on the fleet. The crucible was a pathway between the galaxy and unknown worlds, possibly another universe. Vader had a strange vision of a blue sword, and reached out to it. He ordered his captain Wermis to hold the fleet behind after having this vision. Vader called out to his apprentice Galen Marek, also in the area, through the Force. Marek was also having a vision, one of a a woman clutching the blue sword Vader foresaw. He killed her with Force lightning and took the sword. Meanwhile, in the physical world, Marek had passed out, and his ship, the Rogue Shadow, crash-landed onto an unknown planet. Marek had awoken and mindlessly wandered to the north. Vader followed him to the planet, meeting up with Captain Juno Eclipse.
This strange imbalance of the two universes was sensed by Yoda on Dagobah, having visions of a warrior killing stormtroopers and Tusken Raiders. This warrior suddenly attacked Vader, and Yoda, materializing in this strange world, was attacked by a monstrous being.