It may be more efficient to use an Undead with greater power. However, there are several benefits to using Elder Lichs. 1st, Ainz can create more if they are destroyed. 2nd, they won't be attacked by unintelligent undead and less likely to be attacked by other undead. 3rd, they appear here naturally, so they are less likely to be connected to the Sorcerer Kingdom. 4th, they can easily move around with <Fly>. 5th, they are considered strong in this world, so they are capable of fighting and can be used to bait unknown third parties. Number 3 is the most important. If strong undead were brought from Nazarick and unlikely found in Katze Plains, any powerful being would be on guard. If you had the choice between being wary of or being looked down on, Ainz would choose the latter. Ainz uses magic to create armor and weapons to return as Momon. Next, he holds a staff in his hand that resembles a skull with a spine attached to it. The Elder Liches borrowed Data Crystals from Ainz