Great God Rank is the highest tiered dungeons within the [Age of Gods Dungeons], these dungeons are most likely controlled by the [Great Gods], nothing definite is known about these [Great God] at this point.

Each [Great God] controls a respective dungeon, hence only 5 exist in the world  (Reference to the religion five supreme gods, hence 5 great gods). It's Difficulty is absolutely is the highest, even 【Heroes】 and 【Great Heroes】 who challenge it get annihilated on the first floor.

The level of a small fish is rumored to be equivalent to a Wyvern's. Also, because they’re small fry, they're numerous.