This episode about undead and spiritual monsters was sourced here!
https://en.m.wikipedia.org/wiki/Revenant
https://mythology.net/mythical-creatures/revenant/
https://monster.fandom.com/wiki/Lich
https://voltor.narod.ru/vr/vr05_03.htm
https://en.wikipedia.org/wiki/Lich
https://mythology.net/mythical-creatures/wraith/
https://en.wikipedia.org/wiki/Jiangshi