Aspect Of Heaviness
Back when Lin Mu had originally birthed his Dao Embryo, he only knew of its name and the basic ability which allowed it to make various forms of earth, like soil, rocks, stones and mud.
Later on, as he learned more about the True Earth Heart, he learned of its Dao Skill. It allowed him to form a Heavy Aura around the Embryo as well as himself, which could extend to a certain extent, slowing down things that came into the range.
Only during the battle with the northern Tribes when he fully activated and used it against cultivators did he realize that there was more to it. His understanding increased even further when he saw the head elder of the Northern tribe use his own earth attribute skill.
It was petrification and would also slow down whoever that was affected by it. The effect of 'slowness' was still there, even though the method was different. Lin Mu pondered on this and increased his comprehension even more.