Brise
All of the party members including the soulbounds except Charon were pulled inside the coffin. If Adrian did not do so, then half of them would have been wiped out. It was also Adrian's first time to deeply appreciate the pocket dimension that he was in.
There were only a few accounts of a Lifeless Lord being born throughout the history of Pandemonium. Each being vastly different compared to the other as the first one to be born was holding a sword which was The Undead King himself before he reached the pinnacle undead species.
Charon's skill Soul Keep is influenced by Adrian's origin magic because undead should not have access to pocket dimensions. Sirius' Phantom Rush is an example of a skill that is influenced by the master. Even Adrian does not know how to achieve this as it was only due to the evolution for skills like this to appear.