This quest appears right after you defeat the azure flame god to complete the game. When you check your email on your desktop you will find a message indicating that the quest shop in the town on the delta server now has this quest enabled.
Normally I find Piros very annoying because of his long drawn out sayings and being difficult at time to see around because of his bulky armor and low camera angle. But in this instance he is crazy as hell and can land multiple persistant blows with his lance weapon.
Once everything is set you go to the area “delta endless corpse’s march” and work your way to Cernunnos on the second floor of the dungeon. In the video I basically run through the dungeon, trying to avoid as many encounters as possible because you won’t get credit for enemy units defeated at the end of the quest anyway.
At the end of the second floor you encounter Cernunnos who has a decent amount of Hp to whittle away. I found the best tactic is just to stand right in front of him and slash away with the sword weapon. When he is about to use his breath attack you can avoid it by executing the twin moons sword strike. The animation sequence takes so long you will avoid the damage as well as the annoying push back effect that follows. By hacking away and taking advantage of the beast limit break he will fal, in no time without too much trouble.
For your efforts you get the rare Black Armor from the battle along with three different status enhancement items from the Quest shop keeper.