Soon after the end of the Battle of Dubrillion, Luke Skywalker conceived a plan for intruding himself into the Yuuzhan Vong's base of Helska IV. The Master would have used an iceborer to dig beneath the surface and reach the enemy base. Skywalker couldn't carry on his mission as Jacen Solo and his sister Jaina decided to take the task for themselves.
Once arrived near Helska IV, the iceborer was dropped off at the planet, but the Merry Miner was engaged by enemy coralskippers. At that time, the New Republic's task force led by the Imperial Star Destroyer Rejuvenator of Commander Warshack Rojo arrived in-system, along with the Millennium Falcon, and Jade Sabre.
However, the New Republic was soon overwhelmed, as they underestimated the Yuuzhan Vong force. The Yammosk was binding the soldiers together telepathically, making them fight as one. With this level of coordination, the Rejuvenator and several other warships were destroyed.
Before the battle ended however, Jacen Solo managed to infiltrate the Yuuzhan Vong base and save Danni Quee. Miko Reglia, however, died saving Jacen. Jacen and Danni escaped aboard the stylus ship, which was picked up by Jaina and brought back to Dubrillion. The remaining Republic forces also retreated back to Dubrillion.
The retreat wasn't long-lasting, however. With Danni Quee, Luke Skywalker, Anakin Solo, and Mara Jade Skywalker came up with a plan to freeze the Yammosk in its own icy water by turning the energy it emitted back on itself with shieldships left over from Lando's enterprise on Nkllon. The Yuuzhan Vong forces, having their fleet of coralskippers spread around after the bigger attack before, were caught off guard.
As the shieldships maneuvered into position, Luke Skywalker took his X-wing towards the planet, having many coralskippers follow him. Jaina Solo, Mara Jade, and Danni Quee were aboard the Jade Sabre, with Jaina piloting, and Mara handling the guns. They flew in formation with the Millennium Falcon, who was being piloted by Han Solo, with Anakin Solo on the guns. During the battle, Mara Jade lost consciousness because of her mysterious sickness, and the Jade Sabre plunged towards the planet. Luke Skywalker, in his X-wing, turned upside down, went below the Jade Sabre, and fired off his repulsorlift coils, pushing the ship back up.
By then, the evaporation was taking place, and working effectively, although some of the shieldships were sustaining critical damage or were being outright destroyed. The plan worked, however. The energy being reflected back on the planet evaporated the water, causing the planet to freeze, killing the Yammosk. The Yuuzhan Vong forces were thrown into disarray by the sudden loss of telepathic communications and were easily picked off. Because the ice expanded within the planet, it exploded, killing Da'Gara and nearly all of the Praetorite Vong.