Covenant: Path of the Dragon
To obtain this acievement and join this covenant, you must go all the way to the end of the Ash Lake. While it is not that hard to get there, it's a long way.
First you must get all the way down to the swamp area of Blighttown, then proceed to the opposite side of Quelaag's. You'll end up facing a huge tree and should see a root going up. Once you get up there, there's 2 invisible wall, 1 around the corpse, then 1 behind the chest.
Now you're in The Great Hollow. Make sure you use the bonfire and rest there, just in case... make your way down the tree branches and fight the black frog, be careful their breath will give you a curse reducing your hp by half. When you reach the bottom, you'll have some mushroom, just run by them. Once you're out, you should in the next area.
The Ash Lake, there isn't much here, except a miniboss and some multi-legged clam. When you come in, you should see a bonfire on your right, it's not necessary to use it, but if you want to be extra careful you might as well get it. In that case, you'll have to run all the way back up when you want to exit instead of simply warping. After that, just follow the "sand" trail while avoiding the hydra and the 2-3 clam. Never leave the trail and at the end you should meet with a dragon and a bonfire. Talk to the dragon and you'll get this achievement.
He'll offer you to join the covenant, if you do so, you'll get an item called dragon head stone. Remove your helm, use the item and you'll end up having a dragon head. If you use X while having the dragon head, you'll breath fire. Note that if you want to get rid of the head and get back to wearing a helmet, you have to die.
I'd like to had, to rank up in this covenant, you need to donate dragon scale. In the zone, there's 5 to be found, 3 from corpse lying around the zone and 2 when you kill the hydra.
If you're going to down vote, at least say why you are down voting,,,