Mortal —

Skilled warriors that typically rely on a weapon or external entity for their power.

Magus —

Warriors beyond mortal, with some glaring factor that puts them beyond the scope of a normal person, e.g. magic, super strength, speed, etc.

Harbinger —

Powers to rival an entire army or possess some other power on that scale. Human frailty or some other weakness prevents them for being transcended tier.

Transcended —

Beings that can destroy cities or do things beyond the normal realm of possibility. They can endure far more than a harbinger and are practically immortal.

Cosmic —

At this point, a being must be strong enough to impact an entire planet. Characteristics include: immortality, near-invulnerable, and immensely strong.

I won't be using power levels like, "oh hey Azrael has finally reached the harbinger level" or something like that. Nor will I be doing something like "he's a transcended being", it's boring and cliche. I want it to be up to you to decide what power level the characters are at. It won't be outright stated. ;)