Dark Souls

This achievement is for discovering the Covenant: Blade of the Darkmoon, which is a fairly stylish choice if you're keen on flavored PVP. Members of the covenant invade 'guilty' players--i.e. those who have accumulated sin by invading other players, breaking their covenants, et cetera. In order to join this covenant, you're going to have to venture to Anor Londo after Sen's Fortress--which you can't reach until you've rung both the Undead Parish bell and the Queelag's Domain bell.

Even with both bells rung, there's a little bit more prep necessary before you can chase this covenant and it requires a trip down into the Catacombs (which is located past the graveyard adjacent to the Firelink Shrine). Roughly 2/3rds of the way through the Catacombs you'll find a fairly easy to spot crumbly wall which you can bash through; most illusory walls are more subtle and vanish--this one is literally just loose bricks that you can knock out of the way.

Behind the wall at first blush it'll look like a scary black abyss and you'll hear some skeleton archers--but just inside there's actually a ledge ringing a dark room (with the archers hanging around being pests). The drop is actually not too bad if you don't want to take the ladder, but there -are- skeletons at the bottom so for the sake of sparing headaches you're best off clearing out the archers before you venture down (as they'll also try to shoot you when you decide to climb back up.)

From the bottom of the chamber, you've got a short jaunt before you find a partially open tomb beneath a big statue--and in it, you'll find the Darkmoon Seance Ring. This ring is the key to getting access to this tricky covenant. If you haven't actually ventured to the catacombs before deciding to pursue this achievement, I strongly recommend you also secure yourself a divine weapon first as well to save yourself some headaches--I've put a pretty lengthy explanation for acquiring one in the Rite of Kindling comments if you want to peek.

Once you've got the Darkmoon Seance Ring, you're ready to find the covenant in Anor Londo. The location is inside the twisting / rotating connection tower at the center of the zone--when it is in its lowest position, head to the very bottom of the stairs and you can make your way down to a room with a bonfire and a very large statue. If you wear the Darkmoon Seance Ring, that statue will disappear and you can head downstairs to a secret area with a fog door.

Important: DO NOT pass the fog door if you want to score membership to the Blade of the Darkmoon Covenant or at the very least the achievement; you'll hear a voice when you approach it, Gwyndolin--who will question why you're here and put out a warning. What you want to do is approach the prayer mat in front of the fog door and kneel in prayer--that will identify you positively with Gwyndolin and she'll give you the option to join the covenant then.

As with all the covenant achievements, you only need to get to the actual prompt for it to unlock--you don't actually have to join or abandon your current covenant if you've got one if you don't want to. Blade of the Darkmoon is a PVP oriented covenant--joining, you'll be given another ring and a Blue Eye Orb.

The Blue Eye Orb allows you to invade the realms of guilty players as mentioned before--and it is re-usable any number of times; if you invade while wearing the new ring, the neat thing is that it won't announce to your target that they've been invaded--surprise party! You'll also appear as a blue Phantom, which is pretty neat.

If you haven't gotten far enough in Anor Londo to access the rotating platform, you've just got a short sequence of balancing acts to get there:

Riding the elevator down from the starting area, you're going to need to make your way up an archway connected to a small drop-off to your left when you walk out the base of the tower; this will lead you into the rafters of the cathedral where you'll have to fight the Altair fan club (they are painting guardians, but they all look like they want to cosplay Assassin's Creed anyways).

At the very end of the rafters section, go towards the right, climb down the ladders / stairwells and you'll eventually exit the right side of the cathedral on a platform with a lever for summoning the rotating tower. Hitch a ride and make your way up--just be forewarned that there's a gargoyle hanging out that is basically a copy of the Undead Parish gargoyle boss looking to give you a hard time.

Note that proceeding past the fog door in the hidden shrine initiates an optional secret boss fight with Gwyndolin--but doing so will forever lock you out of the Blade of the Darkmoon covenant (at least on your current playthrough) or break the covenant if you're already in it.

Happy hunting!

Hey all, just a video to help show you where your going with Gaist Heidegger guide for this one. I also included where to grind the Souvenir of Reprisal for ranking up the coven. Hope it helps!