There's lots of odds and ends in the Necromancer's arsenal, and many of them can be potential rules headaches. They go here.
What are Souls good for?
As a Necromancer Wizard, you will often end up with the souls of your enemies lying around. While in your possession, the people whose souls you have can’t be brought back to life by normal means, but they can be used to get in your stuff in other ways. Souls, therefore, are basically a liability to keep around the house, and should be disposed of as quickly as possible. Fortunately, a soul can be destroyed by using it as a spell component or item creation component. The benefits are small (you get like 10 bonus XP or a +10 bonus to a spell resistance roll), but a destroyed soul can’t be brought back to life by any means. That’s good times.
If you want to get souls in your possession, there’s the old standby of Magic Jar. But if you want a little more security in your life there’s Major Creation. It can produce special materials, including thinaun (from the Complete Warrior), a metal that traps the soul of anyone killed next to it. The metal evaporates after not very long, but that’s plenty of time to destroy the soul utterly casting a Chill Touch that is virtually impossible to resist.
Becoming Undead Yourself
There are a number of Undead templates that can be added to your character, with variable costs. Some of these templates have a substantial cost now and no cost in the future. Some templates have a huge cost in the future and no cost now. Which you will want will depend entirely upon how long the game is going to progress. Becoming a Vampire costs no XP and makes you lose nothing at all – but you also gain no XP for doing it and your rate of XP growth goes down and your ECL is five levels higher. So if you become a vampire, you’ll never gain another level for the entire duration of the campaign – which is no cost at all in a one-off game. On the flip side, becoming a Necropolitan costs you a level right now (it can’t cause you to lose 2 levels. If you’re 2nd level when you use the ritual you die, and if you are 3rd level or higher the 1,000 XP loss isn’t enough to make you lose 2 levels. I don’t even know why that rule is in there), but since you’re adventuring with characters who are higher level than you, you’re gaining more XP than the rest of the PCs. You’ll catch up in a few levels, and then have all the power for nothing.
Liches get all the fun and all the women, but it is up in the air as to whether you are supposed to pay levels in addition to the massive GP and XP cost. If your GM plays it that way, don’t be a Lich. Otherwise, do it. A Dread Necromancer looks like they hand out Lichdom for free at 20th level, but the class is only 8 levels long so that ability doesn’t really exist. The fact that there aren’t any good class features at level 9,10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 completely invalidates the genuine awesome that exists at level 20. You could have had the 10th level of a transformative PrC some time ago.
Once you become Undead, it is imperative that you become Spell Stitched. That gives out Spell-like abilities, and can be a convenient way to get free Animate Dead. You can also go far by making your Raven into an Undead Raven with the Stitched Flesh Familiar feat and then Spellstitching him. Remember to hang a Periapt of Wisdom on your bird just before the template is applied, as the template only checks the wisdom of the creature while it is being written, not the rest of the time.
There are three levels of Fear in the game: Shaken (which provides minor penalties), Frightened (which makes people lose all their actions until they leave LOS of the necromancer), and Panicked (which makes people lose all their actions, move randomly, and drop their swag for the duration). If you can apply a Shaken effect to someone already affected by Fear, they move up one category of terror.
The Precise Rules about Clerics and Domains
Every so often, a Cleric Domain will give out a spell that you have no business being able to cast, either because it isn’t on the Cleric list at all, or because it has an alignment subtype that would normally prevent your character from being able to cast it at all. That’s OK. As a Cleric you have a class feature to be able to prepare and cast 1 spell per level from your domain lists, which trumps any general rules that would keep you from casting it. So you can make Lawful Good Necromancer Clerics if you want. They won’t be very good, because they won’t have Rebuking and such, but if for some reason it’s really important to you, it can be done.
Ghoul Gauntlet screws you. Badly.
Ghoul Gauntlet reduces your undead control limit. Maybe it’s not supposed to, but that is what it says. Here's the exact quote:
No matter how many ghouls you generate with this spell, however, you can control only 2 HD worth of undead creatures per caster level (this includes undead from all sources under your control). If you exceed this number, all newly created creatures fall under your control, and any excess undead from previous castings become uncontrolled
Is that a cut-and-paste error? Maybe. But as written, if you have your caster level in Ghouls and you cast Animate Dead to revive your caster level in gnoll skeletons, all the ghouls go uncontrolled even though you haven't exceeded your animate dead cap. It doesn't say "all castings of this spell" it says "all sources". It doesn't say "the newly created creature", it says "all newly created creatures" - even though this spell only creates one Ghoul at a time. That means that there really isn't an argument that can be made that Ghoul Gauntlet doesn't completely screw your control limit that doesn't fall back on "I'm sure that this is an editing mistake and this spell is supposed to be much better than it is."
And if that's the argument you're making, we can't help you.
Ok, so you’ve decided to build a base of operations. There’s a few things to remember. First, despite what everyone tells you, you are not going to have walls made out of bone or permanently desecrated hallways or pools of blood or any of that dramatic and expensive accessory items of out of The Sims, Necromantic Style. You are going to build it along a few practical lines.
You will have “dead-man rooms”, which are rooms full of masses of uncontrolled undead, and you’ll have taken a feat or spell like Lich-loved so that you don’t have to worry about being eaten when you restock the rooms. Then, when heroes come to bust up your tea-party your “Hive” breaks open and destroys the heroes, and perhaps the nearest city as well despite the number of turning attempts or Command Undead spells they might have.
For your intelligent undead, which are most likely incorporeal, you’ll have deep stone floors and walls so that have space to pop in and out as needed, and even 5’ deep walls for “ghost doors” usable by incorporeal guys. (This takes advantage of the fact that incorporeal creatures can only move 5' through objects).
If your DM is using the optional rules on how masses of undead creates ambient Turn Resistance, then you can abuse the Haunting Presence rules by taking a large number of low-HD skeles and turning them into para-ghosts that mass the area, putting enough necromantic mojo into the air to clot the holy artery of any cheeky bastard with Turning (even you, unfortunately).
That’s about it. Add in a few summoning rooms and a hospital ward to inflict dudes which ghoul fever and/or harvest liquid pain, and you are the Martha Stewart of the necromantic world.
A fun way for Necromancers to boost DCs
The easiest way to boost DCs is to take Snowcasting the Cold Specialization and Improved Cold Specialization feats. If you are willing to carry around ice (like a blue ice lined chest with regular ice), this is a +2 to all your spells for three feats, and your spells are cold subtyped, which is a nice bonus favor for an Uttercold Assault Necromancer.
If you are a Wizard, another option opens up. The 10th level Planar Substitution level of Wizard lets you slap on alignment subtypes onto your spells, and this adds a +1 to caster level and DCs when you cast spells on creatures with the opposed alignment, which upgrades to +2 if the spell naturally has that alignment (like adding Evil to an Evil spell). This is nice, but the real fun is when you get feats like Spell Focus(Evil) or Malign Spell Focus (or both). This adds some nice DCs to all your spells.
Add these two techniques together, which stack with Spell Focus and Improved Spell Focus, and you can take all your feats and set a little fire and dance around it and be the master of Save or Dies at 10th level. Other setting specific-feats can also add to these numbers.
The Deathbound Domain errata and a Desecrate area
Most people don’t even know that the Deatbound domain was seriously changed in the errata, so it up to tell your DM about the change or not. That being said, some people are confused as to how the domain works with Desecrate, as the errata on the Deathbound domain power lets you create up to three times your caster level in undead per casting(instead of your double your caster level), and Desecrate allows you to create up to twice your usual limit of 2 HD per caster level of undead(instead of your caster level). You are thinking “How you they stack, if ever?” The answer is that we go to the rules in animate dead itself. When you cast the spell, you specifically control every creature you animate with that casting – losing only creatures from previous castings. This means that you actually can use you whole 6HD per caster level of animated dead – even though your control limit is only 4HD per caster level. This is pretty neat, as it allows a basic Necromancer to create undead armies in one go that are larger than what he can make in multiple steps. You can also make individual undead that are so large that to have a second undead servitor you’d need a Rod of Undead Mastery*.
A note on Undead Creation with a Rod of Undead Mastery
Remember that undead creation is an instant effect that only checks your “max HD controlled” when you cast the spell, meaning you can cast the spell with the rod, then put down the rod to go to sleep and you won’t have to worry about undead becoming uncontrolled. You can pull similar tricks with temporary bonuses to your caster level, such as with Deathknell.
Using the powers of Stone to Flesh and Polymorph any Object you can create bodies, the exact item you need to be able to animate or otherwise create undead. What actually happens at this point is not addressed anywhere. What does it mean that you have the corpse of a creature that was never alive in the first place? Is a statue of a Pit Fiend capable of being made into elaborate undead forms to get its Wish ability “back”? Noone knows. This is a realm of the rules that aren’t addressed anywhere even a little bit. We wish you the best of luck.
Failing that, a conjuring circle for your Planar Binding spells set in the middle of about 12 killer magical traps is generally sufficient to create any kind of corpse you want. Go crazy.
Ok, Black Sand is a substance out of Sandstorm that’s both a magical location and an actual substance. Normally, you wander the desert for forty years until you find it, then you cry because it sucks for you and your party. In effect, it is an area of sand on the surface of normal sand and it produces magical darkness and a d4 in negative energy damage every round.
Not impressed? While it is nice to have a location that provides small amounts of healing over time to your undead, the really neat fact is that anyone killed by black sand joins the black sand. Since black sand can be temporarily created by a clerical spell, your job will be to find a way to get the spell cast on some normal sand, and then you drag your enemies onto it, thus allowing you the ability to create more black sand. This neatly avoids the problem of finding an initial area of black sand.
From this point on, you can carry around a large amount of black sand in a Portable Hole or something, or you can keep it in a Shrink Item form. Toss it at your enemies in Shrink Item form for its magical darkness properties, or keep it around as perfect healing for your undead after battles (or you, if you are undead or Tomb-tainted).
Necromantic Ballista are hilarious
Heroes of Battle has a fun little option for magical seige engines called the Necromantic property. Basically, you hit an area with a seige weapon shot, then it casts a spell that animates a bunch of uncontrolled zombies/skeles for 10 rounds and they attack the nearest person. For a cost of 3k on the encantment and 2k for initial enhancement, this is a great item to carrying around in Shrink Item form. If you are Lichloved, these guys won't even attack you.