Oh I see. Then what gears i should use? It seems mjol is not the good choice, does it?
It seems the Whitesmith will typically endow with a cursed water first from what I was told. So
that would fix the elemental issue with a Mjol. A DBSS mace would also work fine, I imagine. Beyond
that it'd likely be the typical WS gears. Most of the enemies are large, so an executioner-card guard/buckler/stone buckler
would be the shield of choice. I personally wear a pasana-carded armor down there with a deviling muffler. Vanberk mid would be nice.
You'd want either Eddga carded shoes / or DL Valks because of how mobby it is. If you're soloing, accessories would probably vary.
Then the HP partner will cast aspersio to hurt the Hydros and Detale. So if you're going to cursed water endow then you'd have to
avoid them.
Also...
Sharpshooting snipers also seem to do well down there while mobbing by adjusting their arrows.
You can also technically solo with a paladin with shield chain if they have an Aegis and a quad dragoon (earth petite) mace but
the above two would be much faster and less GJ spammy. I personally just kill until my SP dries out. And if I feel like taking a break I'll have my paladin sit at the entrance strip since dragons only infrequently come that close to the warp.
never tried, but always thought hp with DDdr evang could do the trick there
lots of water there and no need for healing supplies 
You could, but it wouldn't be particularly fast because of the dragon's elemental reduction; it's quite mobby down there.
I went down with a professor's Dragonology skill at max with a DDDr tome, and I wasn't doing too much damage as memory serves. A paladin with shield chain was easily out DPSing me in damage.
