Necromancy as a Power

I like magic as powers. It just feels so straightforward and easy to balance (or at least to keep track of). You have the magic that you have, not some crazy spell list. If you need additional powers, you have rules for stunts. Yet I've never really been happy with just listing allies. So here is a set of powers that lets a necromancer control undead, create undead, and build up massive armies with soft limits rather than hard ones, and without too much hand-waving.

The powers given here are using multiplicative modifiers, which I recommend doing any time you use a powers system.

The Power

Necromancy has magic as its source. It is corrupting (-20%), and suffers all the other drawbacks of magic (-10%) -- it can be dispelled, creates magic noise, doesn't work without mana, and so forth.
Complete Rules for corruption are in horror. Short rules: Take 1 point of corruption for each time the user animates or establishes control over undead, and for each day undead are in his power. Each 10 corruption points becomes 1 Character point worth of disadvantage (or negated advantage) turning the user closer and closer to the sterotypical necromancer: A power mad sadistic maniac without pity, remorse, or judgement. The GM and the player may wish to consult about what changes are made first, but eventally they will run out of changes to make. At such a point the character should probably become an NPC -- unless the character both enjoys the play and is willing to work against his fellow players and play out the disadvantages gained so far. The GM should then treat the limitaton as a pact of sorts rather than continuing to track corruption.

The Abilities

Mind Control (Undead Only -50%, Permanent Duration +150%, Conditioning +50%, Necromancy -30%) [30]
This is required to control the undead you create. It also allows you to control the undead that others create. There are a few things to note about this build. Undead in many settings cannot be mind controlled -- the undead only also includes the ability to control undead in the first place. Also, Mind control has a cumulative -1 per subject controlled, which limits the number of undead controlled. To counteract that, see Ally Groups below. The necromancer may also merely reprogram the undead and leave them, but such intructions may not leave ways by which the undead can be controlled -- a necromancer can order them not to attack those wearing black robes, or to stay near a subject, but not to obey a specific person. If another necromancer tries to take control of the undead, rolls are opposed --- but distance modifiers apply for both necromancers!

Ally Group (minion+0%, 15 or less *3)[varies]
This advantage increases the number of minions a necromancer can manage. undead that match the description of the ally group do not penalize future rolls to control undead. This isn't just about numbers, but also about type: a necromancer who has an ally group of 10 animated large monsters will struggle with 100 animated warriors or with the high point remnant of an ancient hero. Of course, improvising an advantage via a power stunt may be an option for managing all those weak skeletons at once.
Its suggested that most necromancers will want to go for lots of basic minions, but that may be dependent on the setting.
Those with DF 9 may wish to use the 'hordes of minions' rule, as many undead are very low power. Those without it may simply wish to treat undead with a negative point value as having a base value of a third a point -- when they appear on 15 or less they cost 1 point! This is not the DF 9 rule.
This is not quite the standard way that these two advantages interact, but in very close in both spirit and price to how they intereact. The 15 or less reflects the fact that undead have a number of extra weaknesses and ways they can be deprived from a master.

Create Undead [10]
pay 2 FP and roll vs. IQ (or skill in appropriate campaigns) to animate a corpse. The corpse is animated as a standard magically animated servitor for the setting. Creating tougher undead may be possible via rolling at a penalty. In all cases the undead should be somewhere on a spectrum from 'mindless' to 'hostile'. Undead must be controlled to be used.
Several Gurps books have (different) templates that will serve this purpose. A template is provided here, but feel free to use which ever template best fits the campaign. The one statistic that should be paid attention to is the will. Tougher undead should be more resistant to control. If will is not high enough (and the GM feels raising it is not proper) add resistant (mind control) to the template at an appropriate level.
This is a new advantage, completely made up. Ok, not completely. It draws on some elements from the create advantage, though it breaks some very specific rules given in that advantage. This advantage is expected to operate in conjunction with Mind Control to let the necromancer actually control his creations -- without it, the undead arise as independent and hostile beings.

Telesend (Undead Only-40%, Broadcast+50%, Necromancy -30%) [32]
Allows the Necromancer to give commands to his minions mentally, and to receive reports. Occasionally allows necromancers to communicate with each other through their minions.

Healing (Undead Only - 20%, Necromancy -30%) [15]
Allows the Necromancer to repair his minions by dumping dark energy into them. Most undead can't heal any other way. The energy often does less to restore material than to bind that which already exists into place, making the construct even more unnatural. Its often more energy effecient to raise a new corpse, unless you don't have a replacement, are in the middle of a fight, or have a rare and valuable undead you wish to keep functioning.

Other abilities may be added. Death powers  such as draining life are traditional (if debatably a different power). But for working with undead, the above form a solid base.

A Simple Template

Basic Undead [-20]

ST 12 HP 12
DX 9  Will 10
IQ 8  Per 8
HT 11 FP NA

Brawling DX/E DX+2 [4]
Primary Melee Weapon DX/A DX+1 [4]
Backup Melee Weapon DX/A DX+1 [2]
Skill reflecting former life [1]

Unliving[20], No blood[5], No brains[5], No eyes[5], No vitals[5], Immune to Metabolic Hazards[30], Doesn't Sleep[20], Doesn't Eat or Drink[10], Digital Mind (undead) [5], High Pain Tolerance [10], DR 3 (Semi-ablative, tough skin without flexible) [9]
Appearance (Monsterous) [-20], Automoton[-85], Unhealing [-20]

This template represents a freshly animated corpse -- a zombie, if you insist on that terminology. As the corpse rots away, it becomes more skeletal. In any case, the corpses skeleton is what need to disabled. The rotting flesh is only so much ablative meat, though it doesn't hurt to have bones wrapped in something. To make a skeleton, remove HP and the ablative DR. Intermediate stages are encouraged! A bare skeleton should have no ablative DR and have lost 25% of its HP.  The skill reflecting the former life should be mostly flavor: a peasant is likely to have farming, a noble riding,

Better undead can be based on this template. One simple adaptation is to make them bigger. Sometimes this means just grabbing an extra large farm hand, and sometimes it means animating a 2 ton monster. Upgrading the stats and skills of the undead on creation or over time should be possible as well. An old favored servant of a necromancer may have grown into something more than a simple animated corpse, or animating a great hero may yeild a powerful servant. Watch the ally group advantage though! a necromancer may not be experienced in managing such powerful allies! Such undead may be more trouble than they are worth if the necromancer only has the ally group for basic undead!

Use in the Campaign

Ally groups are fairly cheap, and what's more, they scale exponentially: The difference between 10 basic minions and 1000 is only about 12 points. Even if you're using quarter point value undead, thats 36 points -- kust over the cost to buy control(undead) in the first place. Just because you can buy the ally group for that many minions doesn't mean the necromancer gets that many minions. They need to steal or create the minions. The ally advantage doesn't do anything to prevent your own minions from being destroyed. High end necromancers should improve their Mind Control (Undead) to have greater range, and increase talent to win fights with rival necromancers.

Necromancy is the traditional realm of NPC villians, rather than PCs. This build can certainly be built that way. Among other things, it gives mechanisms for Necromancers to steal each other's servants and to talk with one another (telesend). On the other hand, this build also gives PC's the ability to 'play with fire'. A PC necromancer can be an effective tool against other necromancers, but at what cost?

Have fun with your lords of the dead!