User blog comment:Matsczon/What is that?/@comment-5264386-20130210003540/@comment-5264386-20130210011017

There is a hidden bonfire in Darkroot Garden, near the Crest of Artoias door. But the Moonlight Butterfly is pretty easy, so long as you have a good magic blocker.

Was he moving slow as fudge? If so, that shine effect was Iron Flesh, a pyromancy which improves your stability and defence. You can buy it from the pyro trainer in the Depths once you rescue him, and he returns to Firelink Shrine after you leave the area.