While Lin Mu's Tyrant Bull Marrow Secrets had regressed due to saving Lady Kang, his Three Apertures Invoking Technique remained intact. It was still at the Aperture Creation Realm, with Lin Mu having already formed three apertures. However, unlike the Tyrant Bull Marrow Secrets, this technique wasn't primarily focused on physical prowess.
Instead, the Three Apertures Invoking Technique excelled at supporting other body cultivation techniques by providing exceptional capacity for storing Immortal Essence. In essence, it acted as the "fuel tank" for the Tyrant Bull Marrow Secrets. With the regression of the latter, the former's utility had been limited to preserving Immortal Essence, which was why Lin Mu could still execute techniques like the Mountain Collapsing Fist using Immortal Essence. Without the Three Apertures Invoking Technique, his attacks would have been downgraded, relying solely on Vital Energy and limiting him to the Boulder Collapsing Fist.
