Cybers use cybernetic implants to mimic the power of Mystics. They are rarely as strong as Mystics of the same stage, but are far more numerous.
The power rankings of Cybers are determined by the tier and grade of their cybernetics. Each tier is equivalent to a mystic stage, while grades go up to three, and determine the power within that stage, much like the cores do for Mystics.
Unfortunately, a Cyber is only actually equivalent to a Mythic, when all the important parts of their body have been replaced by equivalent cybernetics, which is why Mystics are usually more powerful.
Example:
Tier 1 Grade 1 (TG1) Cybernetics are equivalent to a Core Awakening stage Mystic with all their cores at rank 1.
Tier 2 Grade 3 (TG2-3) Cybernetics are equivalent to a Core Formation stage Mystic with all their cores at rank 5.
Tier 3 Grade 2 (TG3-2) Cybernetics are equivalent to a Core Linking stage Mystic with all their cores at rank 3.