Undead come in a variety of types. From the essentially annoying (Skeletal Wariors) to the truly deadly (Vampire Ancients and Ancient Liches). They can be encountered above ground, below ground and under water.

Skeletal Warrior: (Armor 2, Health 17 to 66, Damage 5-15) They hit slowly and do not have a missle or magic attack. They’re also very light. If you can position yourself just right you can hit them from the front and inflict damage when they slam the wall. In theory, edged weapons only do half damage. Once you’ve got a few levels they’re strictly an annoyance. Treasure is a few coins, weapons and armor.

Zombie: (Armor 0, Health 52 to 66, Damage 15-50/Disease) They hit very slowly, but they hit hard. They’ve also got a lot of hit points. Don’t try to stand toe-to-toe with them at lower levels.  Either I've been very lucky or the disease part is wrong, but don't be surprised if it happens. Treasure is money and a couple of armor/weapons.

Wraith, Ghost:

A spell attack followed by melee. Wraiths like to throw little fuzz-balls at you. I haven't noticed any effect from them hitting. Ghosts like "Wizard Rend". You’ll get to know these guys very well if you spend much time in Daggerfall between 7 pm and 5 am. You need Silver or better weapons to hit them. They move quickly, but have a real problem with corners. If you can get them where they need to go around a corner to get to you, it’s best to use missiles. They’re very difficult to see in dim conditions or after dark. Wraiths have dancing spots in them, but ghosts just have the red eyes. At night they’ll turn kind of purple if you can get a light behind them. Treasure is an iffy proposition (most of the time they don’t have any). When they do, it’s usually one item: money, armor, weapon or ingredient.  I have picked up the occasional magic item from them, though. You can pick their pockets (go figure).

Mummy: (Armor 2, Health 17 to 66, Damage 5-15/Disease) Hits pretty decently and the possibility of disease can be a major pain.  Decent treasure if you like money and the occasional ingredient.

Vampire: (Armor -2, Health 28 to 154, Damage 20-50/Spell/Disease) Likes to sling fuzz-balls at you (Sleep, I think) and then close for melee. They’re all female, they hit slowly and don’t hit very well. Their biggest weapon is their chance of infecting you with vampirism. Fortunately you won’t run into them until you’ve got the levels to handle yourself. Treasure is money and lots of ingredients. Occasionally they’ll have miscellaneous items like a holy dagger or holy tomes (don’t ask me why - this is one of those illogical logic things) or a weapon.

Vampire Ancient: (Armor -5, Health 30 to 170, Damage 20-60/Spell/Disease) A very nasty character. Unless he's pre-placed, you probably won't run into him until you're well over 10th level. He likes spells that can put a severe hurt on you (Paralysis and Shock are his favorites). He hits VERY HARD and closes very fast. Spell Reflection is a must with this guy and you must have Mithril or better weapons to hit him. Treasure is LOTS of money and ingredients with an occasional weapon or miscellaneous item.

Lich: (Armor -10, Health 30 to 170, Damage 70-100/Spell)  I’ve never encountered a lich underwater unless I knocked him there first or he was a quest object, but all things are possible. Essentially he’s an undead version of the Spellsword or Nightblade. He hits very hard, though. Spell Reflection is helpful (he likes Shock, Fireball and Wizard Rend), but healing and good weapons are more helpful.  He's not too picky about where he slings his spells, so it's not unusual that he will blow himself up while trying to get at you.

Ancient Lich: (Armor -12, Health 30 to 170, Damage 70-100/Spell)  One tough customer. Heavy-duty spell attack (Shock, Fireball, Toxic Cloud, Lightning, Wizard Rend) and very good melee skills. Not for the faint of heart or low of level.  Mithril or better weapons to hit him.