Upper-Level (or high-level) is a term used to classify powerful magical beings, such as witches, warlocks and demons. Generally, upper-level beings possess exceptionally strong powers and a high resistance to harm, making it difficult or even impossible to vanquish them.
Upper-level demons rank higher in the Demonic Hierarchy and can rise in power by destroying good and promoting evil. Specifically, the members of the Ordo Malorum are referred to as generals of the demonic legions.
Demons can achieve an upper-level rank by collecting more powers. The demon Zahn achieved this by collecting powers through soul trading.