Roar

The power of the Bloodline Curse contained within Solan's soul had already become impure when the skeleton devoured him. And Baiers, who was possessing the Desolate Overlord's Incarnation, used the Bloodline Curse as a medium to transfer his soul into the skeleton, giving rise to the Regeneration phenomenon.

At the critical moment of the fusion between soul and body, just as Baiers reached Heaven Rank, the trap Lin Yun had set up was activated, causing the fusion to fail and the skeleton to suffer from the aftereffects, his power greatly falling from Heaven Rank to below level 38.

This was also the reason that Lin Yun had kept Solan alive! After all, in the 10th Floor of the magic tower, Solan used a Dragon Breath to try to kill him. With Lin Yun's character, he would never be able to tolerate such a threat and should have eliminated Solan.