Thats quite the expensive and heavy trick haha. Gold is never really an issue at this point of the game anyways i guess. All vocaions can Benefit from the periapts though and the Cannon is the best bet for a mystic knight, possibly with a trance. I tried it with a MK too and it was hard to plant the cannons without him warping to me and readying his scythe or lantern.
I've never tried the holy water before if that works that'd be your best bet. Stun, plant cannons, pop 4 demon periapts (Matk up 20% 60 seconds x 4), and start the mayhem.
One thing that also helped me a great deal was wearing the ring that doesn let me get drenched. (Always lantern light) and having the Elite Lantern that i found in Bitterblack (much larger area coverage.) So you dont get caught off guard in the dark. its very useful in that place.