Proper Care and Feeding of SkeletonsEdit
Look at the stats of every monster you ever kill. Look at its hit dice first, and compare its strength, dexterity, attacks, and natural armor compared to its Hit Dice to determine if it is a good skeleton or a bad skeleton. Zombies are usually crap as they only get a single standard action or move action, but they can fly while skeletons can’t. Also note that skeles and zombies keep subtypes except for alignment and subtypes determining “kind” (which I assume is race and things like Angel), meaning that you can animate fire giant skeletons and they’ll have the fire subtype and be immune to fire(and cold, as skeles). Don’t forget that things with a bunch of templates are usually just better than anyone else of their HD. Mostly, you’ll want to reanimate the bodies of fast bruisers.
Eventually you will get your grubby mitts on Awaken Undead and then you can start considering the abilities of dead bodies. Note that the Spell Compendium version of Awaken Undead gives back feats and skills to your skeles. The problem is that your DM will decide if you pick those feats and skills or he does, since its not mentioned in the rules, meaning they might have awesome fighter feat chains that you pick or complete crap like Toughness taken seven times that your DM might pick for ease of use.
Out of the box, skeletons “retain any extraordinary special qualities that improve its melee or ranged attacks.” Now, that’s a straight DM call, but it nominally means that things like Ettins keep their hardcore two-weapon fighting. Zombies do as well, and they keep their flying at the cost of only getting one action a round; this means that unless you want a dragon to fly you around for transport, you shouldn’t make them.
Coincidently, Wizards get Animate Dead at the same time they get Lesser Planar Binding, meaning they build a “trap room” in their lair with loads of magic traps and a summoning circle, automatically killing anything they summon. Then they animate those powerful outsiders and elementals who have a great HD to stats ratio.
The ideal way to fight with skeletons is to keep a small and elite cadre of pimp skeletons. Boost them with spells, equipment like armor and magic items, and heal them between battles. Some people like massive undead armies, but that kind of thing pisses off DMs and fellow players and is actually not very cost-effective in a world of area effect spells. Your DM will start busting out ways to clear swathes of your undead and your pocketbook will suffer, or he’ll find ways to neutralize the bulk of your army like making your adventure only accessible by flying or teleport. You are better off with a few really good undead and you bring them back occasionally with Revive Undead and/or upgrade them with the Spellstitched template. With the Uttercold Assault Necromancer build, you can almost be assured of never losing an undead except to lucky Save or Dies.
Dragons deserve their own paragraph. Normally, they blow because they have high HD and have a bunch of abilities that don’t come with the MM templates; however, if your DM uses the Draconomicon, you can get the awesome Skeleton Dragon and Zombie Dragon templates. The important thing to note is that these guys don’t cap out at base HD of 20 for skeles and 10 for zombies, meaning you can get very, very large undead this way, and that’s so good that your DM most likely won’t let you do it (even though its possible to create up to four times your caster level of an undead if you use the errated Deathbound domain and a Desecrate area). It breaks down like this:
Skeleton dragons lose all their wicked natural armor, get bonus HP equal to twice HD, and get the default skeleton natty armor, but they keep Ex Special Attacks, and they can’t fly. Except for the HD cap removal, this is in all ways worse than using the old rules for skeletons with an Awaken Undead.
Zombie dragons keep half their natural armor, get bonus HPs equal to twice HD, keep their breath weapon at half strength, and lose any Cha-based special attacks. This is actually kind of awesome, even with the usual zombie single action. You can potentially choose a really big dragon, animate it, and it will be an actual tank with large armor, HDs, HPs, and with Awaken Undead it will have mass of skills and feats, effectively becoming an actual vehicle for your party to fly around in. As an example, a 10th level Necromancer (with Corpsecrafter, and in a Desecrate area with altar) can animate an Adult Green dragon (CR 13) that is Huge with 20 HD, a BAB of +10 with a Str of 27, and an average of 250 hps, though its AC is only 17, meaning you’ll need to give it AC items. Ideally, you want to animate a Silver Dragon, as the DC on its paralyzing breath is based on its HD, meaning a 19 HD Young Adult Silver Dragon becomes a Zombie Dragon with a DC of 20 on its breath weapons. Also note that with the Spell Compendium version of Awaken Undead cast in maximized form, our Adult Green Dragon is looking at 96 skill points with skill maxes of 24 (with dragon skills in-class) and 7 feats.
A Note on the Power and Hit Dice of the UndeadEdit
There is no relationship between the hit dice of an undead monster and its relative threat level. Heck, undead creatures aren't even very well priced out for their CR, their Hit Dice appear to have been selected by consulting a dartboard. Perhaps the worst offender as far as low-CRs is concerned is the Ephemeral Swarm from the Monster Manual 3. It's a 90 hit point swarm that is incorporeal and does a d6 of Strength Damage every round in an area of effect that always hits and allows no save. It's CR 5, but is individually capable of killing many high-level parties all by itself. As far as hit dice are concerned, let's just leave it at the fact that a Hulking Corpse has more than twice the hit dice of an Atropal Scion, despite being very much inferior over all.