Iron may cause your stools to turn black, an effect that is not harmful. If your doctor has prescribed this drug, remember that he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
In the Reeking Cave, visited during the quest Diplomatic Immunity, there is a Dark Elf corpse. In Darkshade, southwest of Windhelm, the body of a dead female Dark Elf can be found at the back of the cave near the bottom of the ramp that leads to a chest. A permanent corpse of a Dark Elf can be found at Evergreen Grove. At The Ritual Stone there is normally a Dark Elf Necromancer who can be killed and then have her blood harvested. Drelas Cottage, on the opposite side of the mountain to Morthal, contains a hostile Dark Elf mage named Drelas.
Discover Darkwraith covenant. This covenant requires a bit of planning and is very easy to miss. You need to talk to Kaathe to get the option to join this covenant. Kaathe can be found in the Abyss in front of the bonfire after defeating the Four Kings (see corresponding achievement if you're having trouble with that).