1. Equip your bow in the right hand, talisman in the left. Don't need a shield or secondary weapons. Equip your bow and arrows.
2. From the Nexus, warp to the Adjudicator Archstone
3. Sprint straight ahead down the stairs and STOP when you get near the edge before a small drop
4. Immediately tap L1 to go into precision aim mode. Press R1 to ready an arrow. Wait about 2 seconds and you'll see a manta come into view from the right.
5. If you aim through an opening in the roots hanging from the ceiling, or just to their right, release the arrow the second you see the manta in your peripheral.
6. Jump down and head down the passage, passing by Graverobber Blige on your right. Go through the doorway and STOP! You'll be near an edge. Tap L1 again, look down and shoot the reaper. As soon as you release the first arrow, shoot again. Don't worry, he'll recover from the first arrow before the second arrives. Note: A Lava Bow will kill the manta in 1 shot and the reaper in 2 shots if you use Heavy Arrows or Fire Arrows.
7. Run down either path next to and above the Reaper, when you are almost above his corpse, jump down (it won't kill you, don't worry).
8. Collect his drop and Evacuate back to Nexus.
With a few practice runs, you should be warping back to the Nexus at about 40 seconds. If you have to use the archstone, about 1 minute. With the suggested equipment, you'll get 1647 souls if you kill the manta in the first shot (otherwise, 1372) and you'll get a total of 6060 from the Reaper and his minions, for a grand total of 7707 souls in under a minute, plus some Darkmoonstone. The best part about this strategy is there is virtually no danger to the player!
Assuming you complete most runs in 45 seconds, you can bring in over 600,000 souls per hour.