Means of measuring enemy HD

[Jowgen]

So the Know Greatest Enemy Spell lets you determine enemy CR in 4 broad categories, akin to how the sense motive use in CA p. 102 lets you assess enemy CR in relation to your own level/HD in similarly broad categories (and subject to variance).

Meanwhile, the MotW spell Power Sight gives you a single enemy's HD while the Sense Motive use in OA p. 58 gives you the target's "Level" on a simple DC 15 check (arguably being a better option than the CA version in virtually all scenarios).

Can anyone think of any other methods to deterimine this sort of information? I am mainly asking for the purpose of finding a way to see how many Negative levels a target can suffer before dying on you.

[Thurbane]

Since Knowledge checks for info on creatures are based on their HD, you can "reverse engineer" your check result to estimate approximate HD.

A bit wonky, but it kind of works.

[BowStreetRunner]

I've used Detect Favored Enemy to determine the exact HD of a creature before. The main issue is that it only works on favored enemies.

[tyckspoon]

You can use an Appraise check to determine something's CR based on the rules for slave value, but there's only a loose association between that and HD.

[BowStreetRunner]

You can use an Appraise check to determine something's CR based on the rules for slave value, but there's only a loose association between that and HD.
Plus you need a full minute to complete the check. So generally not very useful in combat. However, I'm going to make a mental note of this particular trick, as there are going to be times when it could come in handy.

[Unavenger]

Since Knowledge checks for info on creatures are based on their HD, you can "reverse engineer" your check result to estimate approximate HD.

A bit wonky, but it kind of works.

You can do the same with truespeak, so long as the target doesn't have a challenge rating, and you can attempt this more than once (also, you don't need to be able to see the target, so if they run away you can keep trying to pronounce their true name until you work out their HD or CR, as appropriate). Sorta wonky though.

You should be able to do something similar by observing the results of a successful colour spray or similar spell - especially a spell like hypnotism which affects creatures in the order of their hit dice.

[Doug Lampert]

The rules don't tell you how it's done, but the spell Trap the Soul has the following text:

Material Component
Before the actual casting of trap the soul, you must procure a gem of at least 1,000 gp value for every Hit Die possessed by the creature to be trapped. If the gem is not valuable enough, it shatters when the entrapment is attempted. (While creatures have no concept of level or Hit Dice as such, the value of the gem needed to trap an individual can be researched. Remember that this value can change over time as creatures gain more Hit Dice.)

So there is some way to "research" this.

[Thurbane]

Cold Iron Warrior (http://archive.wizards.com/default.asp?x=dnd/fey/20040507a) gets detect Fey, which basically works like Detect Undead, but with Fey. (Detect Undead can give you a ballpark figure on HD ranges).

I'm pretty sure there are other classes and abilities that mimic Detect Undead, too.

Detect Undead itself won't be much use for the OP: negative levels and all that...

[Arcanist]

Sense Motive from Complete Adventure lets you figure out their CR


Assess Opponent: As a standard action, you can use Sense Motive to ascertain how tough a challenge an opponent poses for you, based on your level and your opponent’s CR. This skill check is opposed by
the opponent’s Bluff check. To attempt this task, your opponent must be visible to you and within 30 feet. If you have seen the opponent in combat, you gain a +2 circumstance bonus on the check.

I once made a magic item in a homebrew game that combined a few spells like Arcane Sensitivity (Shining South), Know Bloodline (Lost Empires of Faerun), and a few other divination spells that you mentioned to formulate a rapsheet of every low-level magic user with an int above 3 in the world. It included another spell called "Identify with Flame" that I can't exactly remember where it is from. It might be Dragon Magazine, or it might be made up entirely. Can't remember.

[Troacctid]

Urban savant from Cityscape tells you exactly how many hit dice a creature has. It also tells you their AC, BAB, feats, DR, saving throws, special attacks, and special weaknesses. Requires a move action and a DC 15 Knowledge check.

[Kalkra]

Easy Math from Song and Silence might work. It doesn't really clarify what you can and can't calculate.

[Jack_Simth]

Magic Jar (http://www.d20srd.org/srd/spells/magicJar.htm) can do it:

While in the magic jar, you can sense and attack any life force within 10 feet per caster level (and on the same plane of existence). You do need line of effect from the jar to the creatures. You cannot determine the exact creature types or positions of these creatures. In a group of life forces, you can sense a difference of 4 or more Hit Dice between one creature and another and can determine whether a life force is powered by positive or negative energy. (Undead creatures are powered by negative energy. Only sentient undead creatures have, or are, souls.) (Emphasis added)

It takes some setup, but it goes like this:

You get a large number of creatures of known hit die totals, which are expected to come close to the HD of your target. One creature each, of hit dice 1-20, say.

When you look at them via Magic Jar without your target present, you'll see:

One creature (Creature 1) has three creatures that are just as weak, and 16 that are stronger. Creature 1 has one hit die.
Another (Creature 2) has four creatures that are just as weak, and 15 that are stronger. Creature 2 has two hit dice.
Another (Creature 3) has five creatures that are just as weak, and 14 that are stronger. Creature 3 has three hit dice.

... and so on. Starting at creature five, there's both "weaker" and "stronger" counts (1 and 12, respectively, with 6 that are about as strong). The "6 that are about as strong" stays constant while the weaker number goes up and the stronger number goes down. The count of "stronger" hits 0 at 17 hit dice with this setup.

Now we add the opponent into the mix. If the opponent has 24 or more hit dice, he's off your charts - stronger than all of them. At 23 HD, he's equal to one, and stronger than 19. At 22 HD, he's equal to two, and stronger than 18. At 21 HD, he's equal to three, and stronger than 17. At 20, you've got two in the group that have 16 weaker than them.

You can get a resolution of a single hit die, that way. But you have to drag around a menagerie. Fortunately, Magic Jar is a nice spell to have anyway.