I have noticed that if I do not take care of my merc he tends to "go on strike" when I need him the most. More than once I needed him in a crowded fight and he just wandered off to smell the daises or fuck some demon bitch. Worst of all, when I fight Diablo he goes and hides behind the little wall that sticks out from the church so he does not get fried.

His gear is eth vamp or Veil of Steel, bonehew, and shaft.