Chapter 1037: When The Sun Comes Up.

The true form that Ragnarok is fighting is not from just any Primogenitor. It is Marlinto's true form. Every Origin god level being has one. It is a form that is the manifestation of their concept. To unleash it is an indication that Origin gods are taking the fight seriously. 

Monarchs don't have concepts so their form is related to the demon god of Carnage in one form or another. This is because they fuse with their domain of blood which came from the demon god. Marlinto's form is special. It is the spitting image of the god of Carnage. 

The red octopus form of Marlinto is very strong and also capable of fighting many opponents at a time. He has the highest regeneration amongst all the Monarchs because of it. That has enabled him to survive ambushes and even kill his ambushers despite being outnumbered. And yet, he is struggling to kill one Ragnarok.