Joining the Dragon Remnants requires you to first reach the Dragon Shrine. When you do, proceed until you encounter a hammer and sword/shield knight together. Take them out, then look for a ledge with boxes. Bust them up, then drop down and follow this path to encounter a hammer-wielding knight. Take him out, then enter the door beyond. Ascend the spiral stairs to encounter a Dark Spirit. Once he's down, you can grab the Petrified Egg off the pedestal in the room.
With the egg in your possession, return to Iron Keep via the Threshold Bridge bonfire. Cross into the keep proper, then make a right. At the end of this hall is the merchant Magerold of Lanafir. Give him the Petrified Egg, and you'll be able to join the covenant.
Members of the Dragon Remnants are all about PvP, but only with each other. Once you join, you'll be able to leave special markings on the ground via the Dragon Eye. Touching these allows you to summon or be summoned into another member's world. Kill them, and you're rewarded with a Dragon Scale.
- Rank 1: Collect and offer 10 Dragon Scales.
- Reward: Dragon Head Stone
- Rank 2: Collect and offer 20 Dragon Scales.
- Reward: Dragon Torso Stone
- Rank 3: Collect and offer 30 Dragon Scales.
- Reward: Black Dragon Greatsword