Welcome, this guide is dedicated to making preparations for joining the covenant, finding it, clearing its exclusive areas and defeating the Darklurker, a boss only found through this covenant.
I have split the guide into several sections that cover all these steps, if you need help with a particular thing, check out the different sections.

Just a heads up, you can acquire the Selfless Giver achievement once you defeat Darklurker. This is the fastest, most non-grindy way to do it too. If you want the Master of Hexes achievement, then maxing out devotion is necessary because Grandahl will only sell a specific Hex once you're rank three. You also get a unique Hex after beating Darklurker.

• If you plan on joining the covenant, it's very crucial to be miserly with your use of Human Effegies. Gaining entrance into the Dark Chasm of Old Areas requires one Human Effigy for every time you go in. The only time it's free is the very first time you go in. After that, the extortionist in the wheelchair will demand payment for having another go.
  
• If you want to save up Human Effegies, but the Hollowing system is giving you too much trouble, the Ring of Binding and Life Ring +3 will heavily counter the max health loss. Ring of Binding is located in the chest the Heide Knight is leaning on right before Dragonrider's boss fight. Life Ring +3 is found in a room with a flaming giant and Bride of Ash after activating the Foyer lifts in Brume Tower.
  
• Fire, Dark and Magic resistances will be very useful against the enemies in the Chasm areas and when fighting Darklurker.
  
• Attention shield users: The Rebel's Greatshield is very useful against the enemies in the Chasms and against Darklurker too. If you want to use something lighter to maintain fast rolls, Drangleic Shield and Watchdragon Parma are your next best choices.
  
• Attention melee fighters: Based on personal experience as well as observing speed runners, The weapon that is most consistently effective against Darklurker is the Red Iron Twinblade found in Shrine of Amana.
  
• Attention magic users and pyromancers: Darklurker is extremely resistant to Magic, Dark, and Fire. He is weak to Lightning however. Consider buying Profound Still from Darkdiver Grandahl if you use magic because it will make Darklurker useless for 30 seconds.
  
• The Black Witch Set will be invaluable against Darklurker (he doesn't deal any Physical damage), but it's not very useful against most of the enemies of the Chasm areas so only equip it right before entering the boss fight. This set is sold by Royal Sorcerer Navlaan in Aldia's Keep. To actually be able to buy stuff from him, free him by pulling a lever on the opposite side of the room and be in Human form. Note that once you release him, it opens him up to invade you in various pre-determined locations.
  
• Load up on Flame Butterflies before entering each of the Dark Chasms of Old. If you're low on them, Weaponsmith Ornifex sells them for 600 souls. To get to her, use the Fang Key dropped by a petrified lion statue near the third bonfire of Shaded Woods.

• The Pilgrims of Dark are a PvE oriented covenant that grants you access to Darklurker.
  
• Despite a clear focus on PvE, there is a small PvP aspect to this covenant. If you use a Cracked Red Eye orb while in the Dark Chasms, you can invade a player also in one of the areas. Defeating them grants you a Human Effigy. You can't rank up by doing this to people though. And of course, you are also fair game to get get invaded if playing online.
  
• If playing offline, Pilgrims of Dark is one of the few covenants of the series where ranking up while offline is possible.
  
• Dying by any means while in the Chasms will return you to your last bonfire and count as any other death.
  
• The enemies in the Dark Chasms of Old can be farmed for Bonfire Ascetics. However, I only sugguest doing this once you have either maxed out devotion or if you have many Human Effigies to spare. Leaving the areas by any means other than clearing them will result in needing to cough up more Human Effegies for re-entry.
  
• Important : These areas are HARD to deal with. The enemies hit very hard, the areas themselves are very precarious, Darklurker is a very difficult boss himself and the locations you find Grandahl in are also fairly dangerous as well. For these reasons, this covenant's content is best saved for endgame or when you're at a point that you feel you're ready to take on anything the game throws at you.
  
• Lastly, if you are familiar with the first Dark Souls, then many of the Phantom enemies are similar to or direct copies of Red Phantoms in the first Dark Souls. Havel The Rock, Undead Prince Ricard and Xanthous King Jeremiah all make appearances here (indeed they may be the same characters from the first game, now consumed by the Abyss), as such, they have the exact same moveset as in the first game.

To discover the covenant itself, you must meet Darkdiver Grandahl in three locations throughout the game: Black Gulch, Shaded Woods, and Drangleic Castle. The specific areas where you find him are quite hidden and can be easily missed so I will include directions below.

• In the green hellhole known as Black Gulch, there are three ledges you can drop down to from the cliff.
  
• The very first one that leads to Lucatiel of Mirrah is not needed for the purpose of this guide.
  
• The second one is located inbetween the two big serpents that pop out of holes in the wall. When you drop down, make sure to drop slightly to the left in order avoid falling of the map.
  
• This second one leads to the room with Grandahl, HOWEVER, do NOT come here immediately, the room with Grandahl is locked behind a door that requires a key.
  
• The third ledge you can drop down to is right before a path that leads to the second (hidden) bonfire of Black Gulch. It is near the end of the area, towards the fog door. Drop down and kill the two Elite Giants there. These two have to be killed for the key. Ranged users may have an easier time here since the giants don't follow you to the ledge. They also won't follow you to the two small caverns in the cave.
  
• After defeating the Giants, go to the second ledge and open the door. Exhaust dialouge with him to progress.

• Once you reach the third bonfire of Shaded Woods, keep moving as normal. Right before Najka, there's two damaged towers and a few planks of wood guarded by two Forest Guardians. You can fall through these planks of wood.
  
• To the right of the first planks and of the towers, there's another, semi-hidden set of planks. Fall through these to find Grandahl here. Once again, exhaust dialouge to progress.

• Once you get to the first bonfire, head into the room with statues that become enemies.
  
• Lure one of the statue enemies to the far-left corner and kill him. This will open the door to the room with a Ruin Sentinel. This room has a hole that drops down to a cave.
  
• There are two rooms within the cave. One room has another bonfire, the second one is the last place where you meet Grandahl. Once again exhaust dialouge. If done in this order(it doesn't have to be), then Drangleic Castle will be the first place you can join the covenant and traverse the first Dark Chasm of Old.

To actually "clear" an area and rank up in the covenant, two conditions must be met:
1. Kill all Phantoms in the area.
2. Light a sconce with a torch.
This is why Flame Butterflies were needed before entering. I'm not entirely sure, but I'm pretty sure any torch you come in with is extinguished before you spawn. Once lit, they will stay lit (but you still have to kill all enemies.)

• There are six enemies in this one. The first one you'll encounter is a tanky, dual demon hammer wielding cheeser that will likely notice you right away. Run back near the start of the area and take care of him there. If you don't, the mage and the King Jeremiah type pyromancer may notice you. He can pull out an Estus Flask to heal so dispatch him when he does.
  
• The mage can be taken care of from the ledge with a bow or crossbow (and should be). He can come up to get into melee range, but this doesn't happen often.
  
• Head on down and take care of the pyromancer. Be warned his attacks deal some serious damage and he also has an Estus Flask.
  
• The path ahead forks in two directions. Head left first and light the sconce. Be careful when walking towards it. Return to the forked path and head right now.
  
• The exit is guarded by three of the same enemies from before. Once again, lure out the tanky guy, then lure out the mage and finally dispatch the pyromancer.

• By far the easiest one. This is the one you want to go to for repeat tries to kill Darklurker.
  
• After spawning you will follow a path with a lot of holes and edges that will obviously kill you if you're not careful.
  
• Eventually, you'll come to a large room with three enemies. An archer, a swordsman and a mage. Try luring them one at a time with a bow or crossbow. If the others notice you, make a tactical retreat back near the start of the area and hopefully get them separated enough to kill them separately.
  
• If you manage to lure just one, you can stunlock them into falling into the pit immediately in front of the entrance to the room. This is almost always the best strategy. Weapons with fast attack animations are best for this.
  
• The mage can't be stunlocked but he's also the weakest of the three so it's not too bad. Just make sure he doesn't stunlock you into falling into the pits with his force spell.
  
• The sconce is in this large room with the three enemies. Light it before moving forward.
  
• Pull the lever you'll soon come across, ride the elevator down and kill the last enemy. He's a heavy dexterity type enemy that can easily stunlock you, so be careful. After dispatching him, head on through the fog gate and consider this area cleared.

• By far the hardest one, prepare your anus for this one.
  
• You will spawn in a weird S-shaped path that must be carefully traversed to further yourself.
  
• After that, you'll come across the Havel like enemy. If you aren't familiar with Havel, then I feel sorry for you.
  
• He is the most dangerous, of the enemies here, try to lure him with a bow becaus it is very easy to get noticed by the Prince Ricard type enemy or by the mage and if they do notice you, prepare to die.
  
• You can stunlock him into falling into a pit, but you better have a heavy, Poise breaking weapon for this. You can also run back to the S-shaped path, jump from where you spawned directly in front of you (unto the path) and hopefully Havel will fall into the pit while chasing you. This is hard to pull off because the AI here isn't dumb. By the way, he has an Estus Flask.
  
• Next dispatch Ricard (guy with the Rapier). Again, try not to get noticed by the other guys. If you do, you can try to run circles around the area, hitting them as you run. This only works if Havel is dead because he and Ricard both have Estus Flasks that they will gladly use.
  
• Once he is done, go to the left, dispatch the mage and notice a very narrow path. Take care when going through here as it's easy to fall off. The sconce will be here, light it.
  
• This small area with the sconce can be used as somewhat effective crowd control if Ricard and Havel are both chasing you. One may fall off, or simply stop chasing you. it's usually Havel, but this is NOT guaranteed to happen.
  
• Once that's done, go to the right, dispatch the only enemy left (take care she can inflict Bleed) and exit through the fog gate.

• Darklurker is one of the hardest bosses in the game. His damage is very much scaled for endgame, so preparations for the fight are essential.
  
• He is very resistant to Magic, Dark and Flame. He is weak to Lightning.
  
• He only deals the same damage types I mentioned above. He deals no Physical damage at all.
  
• By this logic, don't bother with heavy armor. The best clothes you can wear is the Black Witch Set. See Preparation and Information for more.
  
• The fight itself will trigger once all three sconces in all three Chasms are lit. When you try to exit the last Chasm, instead of being taken back to Grandahl, you are taken to his arena.
  
• Any buffs applied to weapons or yourself will not be active if you apply them before entering.
  
• Darklurker has a very varied moveset that consists of different spells he will cast at different times.
  
• His only melee attack consists of a three-strike combo, with the third strike having significant delay that often catches you off guard. These three strikes can be dodged by simply strafing to the left. Getting hit by all three is guaranteed death.
  
• If he begins raising his arms up, but isn't at 60% HP (more on this later), it means an AOE spell will soon come from his body. Get away immediately as this is possibly his single most damaging attack. Once avoided, he takes some time to recover, feel free to get hits in or heal.
  
• If he begins flying upward, immediately get under him. He will begin casting a laser around the arena and being under him is the safest place. While under him, you can heal or try to hit him with some range.
  
• If a portal opens up above him, take some time to heal or hit him. After a bit, he will send an orb into the portal and another portal will spawn in the arena where the orb will exit from to hit you. The channel time for this spell is VERY long so do use the time for something.
  
• His most deadly attack in my opinion, is the homing fireball spell. Around five or six fireballs will appear above him, he will launch them at you consecutively. These fireballs can track you for quite a bit and getting hit by them can result into a quick stunlock and death. Run circles around the arena until the fireballs are depleted.
  
• His only other attack is a weak, but somewhat delayed, lightning spear that can almost always be tanked unless you're very low on health.
  
• The real fight will begin when you get him to 60% HP. He will take about three seconds to split into two. Both have the same moveset I just described, but managing both can be quite the challenge.
  
• While he's splitting, he and his copy can both be hit for extra damage.
  
• If you're comfortable doing so, play unlocked because you'll want to keep them both in your sight at all times.
  
• If you stay close, this will prompt them to use their melee if you're comfortable dealing with that.

• The speedrunner's choice when tackling ol' Darklurker (and for good reason).
  
• Apply Gold Pine Resin right at the beginning of the fight for good measure.
  
• The basic idea here is to stay very close to him, run circles clockwise(left) of him and hit him in between his pathetic attempts to melee you.
  
• Of course, he isn't guaranteed to only melee you, but he is much more likely.
  
• Once he starts splitting, go ahead and get as many strikes in as possible. Oh and only use basic attacks, the strong attacks have too long of a windup.
  
• Once there's two, and if you took the chance to whale on the guy while splitting, he should be pretty low on health. Try to make them stay close and continue to run around both while getting hits in. It is a bit harder now, but they should be close to dead.
  
• If one is stupid enough to start casting the laser or the portal orb, go ahead and just finish the other one off.

Video demonstration of this technique at 2:19:50. Not by video, all credit goes to Distortion2. Check out his other videos if speedrunning interests you. Video insertion was not working. Sorry about that. https://youtu.be/S3_RVVWbS8I?t=2h19m50s

• Alright ranged players this one is for you. Oh and if you wanna pull this off successfully, you better be a roll god (or goddess).
  
• Light Crossbow +10 is probably best here. No bows because they're too slow and require two handing.
  
• Equip and nice light shield in one hand with crossbow in other. Drangleic Shield and Dragon Parma are my choices here.
  
• Equip Throwing Knives as well. No bombs or urns because they're too slow.
  
• In heavy contrast to our melee cheddar, the point here is to stay away from Darklurker, dodge his highly telegraphed attacks and fire stuff at him while he's casting or recovering. This is obviously kinda complicated but it is possible to do without getting hit once, even after he splits.
  
• The hardest attack to deal with is the homing fireballs so try running instead of rolling when he whips it out.
  
• Use the shield if you're not going to roll in time, but otherwise stay mobile.

• For the Pyromancers, equip Chaos Storm, Wilted Dusk Herb, and some running shoes.
  
• There was a previous way to do this with Fire Orb, but they somewhat nerfed that spell, so we're using Chaos Storm instead.
  
• Run around the arena hugging the wall and casting Chaos Storm when given an opening. Obviously, play unlocked because you wanna be as fast as possible and keep and eye on both Darklurkers.
  
• Don't worry about positioning because it's Chaos Storm, at least one will be getting hit.
  
• This is the easiest method in my opinion, but it can feel pretty random. Just keep running, casting, and healing and he'll be down in no time. Oh and use those Wilted Dusk Herbs to replenish spell use.

This section will be continually updated with pictures and videos because it's pretty hard to explain these strats and any future ones I come across in detail with writing. This section was a last minute thing (finding ways to cheese this guy is a hobby of mine) and wasn't originally planned. Stay tuned for more.