That thing is still at the Legendary Level.
Although its size is unbelievably large, it remains at Rank 8 Legend, having not surpassed this level.
Strength and size can determine the level of power, but this isn't absolute; there are plenty of creatures with great size but little strength.
Of course, this guy's terrifying size isn't for show, otherwise it wouldn't seem to be single-handedly wiping out a Nightmare Realm overseen by a Child of Nightmare.
From what we can see now, the Nightmare Creatures within this Nightmare Realm seem to have been mostly devoured by that monster, which is now hammering away at the core of the Nightmare Realm, the equivalent in the Divine Realm would be hammering at Lin Xiao's True Body in the God Country.
"I hope that Child of Nightmare dies soon!"
Only when the Child of Nightmare falls will the connection between the Divine Realm and the Realm slowly collapse and separate.
