The Rotten - Arm Chopping Strategy video: http://youtu.be/DrTqIy8DI4w
Just get close and bait an attack and then run out of his attack range fast. After he attacks go back and poke :) Light armor and long range melee weapon is recommended but not necessary.
"The Rotten embraces all, in the sanctuary for all things unwanted or tossed away."
A hideous monster made of corpses stitched together, that rules the Gutter. It carries a large Butcher's Knife in one arm, and crawls using the arms of corpses where its legs would be. The arms can be cut off to reduce the lethality of the Rotten, preventing it from using the Butcher's Knife. However eventually they will grow back. The left arm will drop a Pharros' Lockstone once cut off.