The Eternal Physique is one of the 12 Immortal Physiques.
The Eternal Physique had no effect on one's cultivation nor any assistance in battles. Instead it prolongs one's life for a very long time. Legend has it that once the Eternal Physique was cultivated to the apex, one could reach immortality. Whether it is true or not the Grand Completion Eternal Physique can live for an extremely long time (at least several millions of years) and doesn't need Blood Era Stones nor require blood force halting; one can wake up whenever they want to.
Eternal Physique cultivators could sleep without doing anything else, and they could wake up at their whim as well. To them, sleep is cultivation. When they are awake, their training halts.
Cultivating the Eternal Physique is a tedious and lonely process, extremely slow, like a crawling snail. For cultivators with the Eternal Physique one generation was a short amount of time and two generations were only the beginning. Only at third generation would they really step into the Physique's basic realm. However, as long as one had enough perseverance and an unwavering dao heart without falling to the temptations of the world, then they would ultimately be able to struggle on.
After reaching the Grand Completion, one can control the flow of time; one moment can be extended to thousands and even millions of years. Anyone trapped inside such flow of time, even Immortal Emperor, as well as all their attacks would be corroded and destroyed by time.