There were three methods for clearing occupied slots.
The first was if the engraved undead died. However, this was extraordinarily difficult. Once engraved, an undead's constitution fundamentally changed.
Whenever one was pushed close to destruction, it would instinctively retreat into its engraving to recover.
Of course, that recovery wasn't free. It continuously consumed Michael's energy alongside large quantities of physical materials suitable for reconstructing a new body. But as long as he could afford the cost, an engraved undead was incredibly difficult to eliminate permanently.
The second method was to release the engraving.
By consuming an enormous quantity of energy, along with blood and suitable materials, monster blood worked particularly well, Michael could reconstruct a physical body for the engraved undead, returning their relationship to its previous state before the engraving.
