Mortal Gods are classified into 13 levels of existence each increase in the level of existence the stronger the Mortal God is and their race also evolves.
level 1 Existence/Normal Mortal
Level 2 Existence/Monarchs, Lords, Saints, and heroes of certain Mortals race
Level 3 Existence/God
Level 4 Existence/God
Level 5 Existence/Serval God
Level 6 Existence/Lesser God
Level 7 Existence/Intermediate God
Level 8 Existence/Upper God
Level 9 Existence/Greater God
Level 10 Existence/Arch God
Level 11 Existence/Sovereign God
Level 12 Existence/Supreme God
Level 13 Existence/Creator God or World God
At this Level Existence system, you will only become a Mortal God when you reach Level 3 existence while the Level 1 and 2 are mortals, to become a Level 3 existence you must have a 100% pure divinity of mortal god, that is why Level 1 and 2 are classified as mortal despite how powerful they get in the future.
example of level 1 and 2 existence was Alien, Human, Dragon, Spirits, Demon, etc, any being that doesn't have any Divinity and have normal strength among their race will fall into this level. some examples so that you can differentiate between level 1 and level 2 existence.
Level 1 existence:
Humans, Elves, Giants, Dwarf, Beast Kin, Mutants, Humans with quirks, Kryptonian that still have not activated the powers of their race, Saiyan that don't unlock the Super Saiyan transformation, Lower ranking dragons, etc.
Level 2 Existence:
High Humans, High Elves, High Giants, Greater Dwarfs, shadow Monarch, Dragon Lords, Demon Lords, Demigods, Heroes, Heroic Spirits, Shinigami in the Bleach series, Super Man, Super Saiyan, etc.
The Universe God Class equivalent in the Level Of Existence.
Lesser God= early stage Level 3 Existence.
Intermediate God= middle stage Level 3 Existence.
Upper God= peak stage Level 3 Existence.
Ancient God= early stage Level 4 Existence.
Level 3 existence
-they have the power to create and destroy Universe in an instant.
Level 4 existence
-they have the power to create and destroy Multiverse.
You're wondering why the Lesser and intermediate are level 3 existence, the factor to become a level 3 existence is not based on the power it is on the purity of your divinity, if you possess a 100% pure Divinity of a Mortal God you will become a level 3 existence.
Each level of existence is divided into 4 stages which are Early, Middle, Late, and Peak. the strength of each stage depends on the Level Of Existence.
Level 3 Existence.
Early Stage= can destroy and create a world.
Middle Stage= can destroy and create a galaxy.
Late Stage= can create and destroy multiple galaxies.
Peak Stage= can create and destroy the universe in an instant.
Level 4 Existence
Early Stage= can destroy and create hundreds of universes.
Middle Stage= can destroy and create thousands of universes.
Late Stage= can create and destroy trillions of universes.
Peak Stage= can create and destroy an entire multiverse.
In the universe of Danmachi, most of the Ancient Gods there is an early stage level 4 existence, but one of the Ancient Gods there is an exception and that is Ouranos, Ouranos is the strongest God in his own Omniverse and he is a level 10 existence.