ARCHIVED Ophanim's Merfolk Death Knight guide
This is a quick guide written by Reddit user Ophanim, so credit given where credit is due.
If you really like the idea of having undead minions but don't enjoy playing a Necromancer, I'm going to make a suggestion. And I want you to consider it because this advice is coming from someone with a lot of experience in playing necromancers (in fact, I have the DDNe high score).
Play a Death Knight. It's all the fun of necromancy without half the work. You can Raise Undead as an AoE, Mirror Damage inflicted on you by others to the source dealer, steal the soul of any intelligent living creature and get an exact copy of them on your side permanently (including most uniques outside of demons/undead), and you'll get free high level undead gifts including a Bone dragon, Profane servitor, and Ghouls. All for the low price of worshiping Yred.
I suggest picking a race that's good with Polearms like Minotaur or Merfolk and learning to use your minions as barriers while you strike at the enemy with reaching. Once you get to Lair you should get your Invocation to 10-12 so that you'll be ready to Soul Steal stuff in Orcish Mines. Aside from needing to use Recall to move your friends from floor to floor this is one of the easiest combos in the game. If you're lucky, you'll get a Bone dragon in Lair and have an easy game until you need to get runes.
Here's a short walk through of how you can play a DK.
At the Start
Start with Merfolk Death Knight. Select Spear as your weapon. Immediately hit "m" for skills and turn off everything but polearms and train it until it reaches 10. Do not train other skills. 10 will come quickly for Merfolk as you have a +4 aptitude.
Approach the dungeon using the following order: Clear floors until you reach the Lair (skip Orcish Mines if you see it first) and clear the Lair, return/find the Orcish Mines and clear those, return to the dungeon and clear floors until you reach Vaults where you can do the first 2-4 floors before clearing your two rune endings in Lair to 4 each, finally returning to the dungeon to clear Vaults to 7, then the dungeon to 26, and finally getting the easiest Lair rune, the harder Lair rune, the Vaults rune, and clearing d:27 and then Zot. You can do Elf (located in Orcish Mines) and Crypt (located in Vaults) as early as Vaults 4, although I would probably leave them until just before doing the runes.
Weapons, Spells, and Armour
Obtain a Demon trident, Leather armour, and all slaying you possibly can. You will want rF+++ and rMut before finishing Zot. You can decide to get spells if you wish but know that you will have limited XP.
Skill wise, after your Polearms reach 10 you can turn it off and replace it with Dodging/Fighting. When you hit Lair you should turn everything off except Traps/Invocation and train them to 10/12 respectively. This can often happen using only the XP in Lair alone. Once you have that finished, you can return to Dodging/Fighting until they max or you find a Demon trident, making it necessary for you to put Polearms at 12. You can swap Fighting out for Polearms if you feel comfortable with your HP or Fighting out for Spellcasting/<x school> if you decide to hybrid (I would stick to Charms, Translocation, and possibly Poison/Conjurations if you want Poisonous Cloud).
Keep your gifts alive. If they are low on HP they can regen just like you -- by resting. The best gifts are easily Bone dragons because of their high HP and high damage, but Profane servitors and Ghouls are both extremely good. It is almost always good to have 1 Profane servitor for the pseudo-EV bonus they provide you and you should learn to use CTRL+T to tell your Ghouls they can equip anything, especially when they'll pick up crossbow.
Your early strategy should be to simply fight anything you can kill like any melee character. Once you can raise undead using Yred's abilities, you can use zombies to help you kill anything scary or to act as blockers while you run away. Avoid using Pain Mirror unless you find yourself in a situation you will otherwise lose (I tend to only pop it when I am not sure if I can kill an early unique or get trapped). You should start getting gifts fairly early and by Lair you can have up to Bone Dragons or Flaming Corpses already. Be wary of hydra (some undead do slashing damage) and anything really big if you do not have a high level gift already (Rupert will annihilate anything smaller than multiple ghouls/servitor). Learn to travel floor to floor by hitting SHIFT+X and then < or > to find up/down stairs respectively, hitting enter to fast travel to the stairs, and then using Yred's recall to pull all your friends to you (and do not take stairs unless everyone is next to you or in contact with someone next to you). Always use polearms and hit "v" to evoke reaching or TAB to autofight (which uses reaching for you), especially if you have undead that can stand between you and the target (it will reach through them automatically).
About Soul Steal
Oh, and about Soul Steal. With Invocation at 12 it will almost never fail. You use it by selecting it and then selecting a HEALTHY (not hurt!), LIVING (no demons or undead), and INTELLIGENT (no animals) target you can see, giving you a few rounds (not many) to kill it. If you do all of this you will get a spectral version of the target that has all the abilities it had in life, will fight for you, follow you across floors, and never leave unless it dies. Early on, uniques are best for this (especially Nergalle, Rupert, Saint Roka, and Kirke) though there are other good choices (orcish sorcerers/high priests/warlords) but later on you will typically be using high level monsters (Titans are probably my favorite but any high level Elf or Draconian Callers will do). You should pretty much always want to have something around.
Mandevil, Merfolk Death Knight - An implementation of this build.