First BC
If your party wants to save time, take the Dvucca Isle staging point prior to the undead swarm besieged. If your server loses that besieged, you can simply head WSW in a straight forward path to the reef zone at F-9 and be at the area where the mobs drop key items.
All party members should have Merrow No. 17's Locket and gear/food that enhances Resist Charm if possible.
Enter the main Arrapago Reef zone from the Mire, and head west towards the map that is marked "B"
You will continue heading in a due west pattern on this new map, head towards the map that is marked "C".
Once in this map, hug the left wall. You will eventually find a zone to the mire that leads to Duvca Isle. (Note, on this map, you may opt to head to the mire zone at F-6 instead to the zone that puts you on Duvca Isle. If you do, you will zone into a different part of the Mire. Just head due south and you will find another zoneline. You will be on the same map of the Reef, but on the north end instead of the south end.)
After zoning, hug the right wall. You will find a new zoneline to the Reef at G-9.
Once you zone, go north. All the mobs here will detect through sneak and invisible. This is the camp for the key items, as those mobs will drop them. You may set up camp at either zoneline, or by the BCNM location. The key items are Merrow Homunculus and Lamia Homunculus.
The BCNM location is on H-8 on that map.
Second BC
Zone into Arrapago from Caedarva as you would for the PUP or COR quest.
Past the first boat head through the Iron Gate at (J-9). A Lamian Fang Key or THF with tools is necessary
Head West to (F-10 and the next Map)
Head to I-11. If you have not picked up the two key items on the way, do so now. If you hear a message involving a woman singing, this is the right way.
Use the Merrow Homonculus to enter this gate (and new map) and head SW towards (G-9) for a new map.
From here head south until you reach an open area. Head either East or west as this area is basically a ring of land. there will be an entrance at either (H-9) or (I-9) and you will see the Tidal Gate. Lamia and possibly Lamia Idolaters near the entrance are True Sight
The 3 NM are Lamiae:
Lamia No. 24 (BLM)
Lamia No. 19 (WAR)
Lamia No. 11 (RNG)
Kill the mobs, if possible, in that order. It has been reported once Lamia No. 24 is down, the other 2 Lamiae will go down quickly. Lamia No. 11 is known to stand and shoot, but is immune to sleep.
The fastest the AC been recovered here was approximately 4H 20M since beastmen took it.