Both times we have killed him, this mob was found up the middle ramp (past the sol elementals) on the way to whatever mini that is. It was in a ring of mephits not far past the click pot up some stairs. Looks like its a random spawn in that ring of 6-7 mephits.
This is a level 68 Enchanter! mob... they will tash, stun, mez, charm and cast a dispell magic that removes your first 4 buffs (they will also dispell their mez'd friends to mix things up a little). They drop the sanguine cap commonly, and the Sol Ro Emblazoned Cloak rarely.