3.5 Knowledge Skills - the obscure ones without descriptors. Let's flesh them out.

[daremetoidareyo]

I've been working on skill guide to knowledge checks. And many of the skill checks are quite powerful, Arcana, the planes and religion taking the top place. They have a myriad of in game uses explicitly outlined. But then, there are some knowledge skills that are nothing more than words between parentheses in a statblock.

Your Mission, Should you decide to accept it, is to bring these obscure knowledge skills up to the same level of utility as the major knowledge skills. For comparison, let's look at knowledge religion: the ability to know a ritual to summon a demon, the ability to exorcise a haunted site or item, identify gods of long lost civilizations, identify gods of other races, understand church and cult structure, know how to identify a few creature types and what their abilities are, recognize a shrine, interpret church doctrine, and something about relics. But what does Knowledge (weaponry) Sword and Fist p.38 do for you? It sure should do something more! It doesn't have to be broken like the sacrifice rules, it can metered out a bit better like the architecture rules for boat building.

So here are the knowledges that I'm most interested in seeing filled out the most:
Knowledge: dragonkind, (tiamat/bahamut statblocks) Manual of the Planes p.118, 133, 172
knowledge: weaponry, Sword and Fist p.38
Knowledge: Streetwise (drinking, flirting, gambling, tailing) Sword and Fist p.10
knowledge: geology, Tiger palace p.4 (statblock):
Knowledge: local bars and alehouses, The fright at Tristor p.31: (statblock)
knowledge: dreams, Epic level handbook p.161: statblock:

The rest can be found on the main page: http://www.giantitp.com/forums/showthread.php?514547-The-Library-of-Knowledge-Getting-the-most-out-of-your-studies/page2 Other standouts include knowledge (literature) and knowledge (alienism).

Questions we need answered
What creature types and subtypes can you identify using your knowledge skill?
What main body of knowledge do you have mastery over?
How do you use this skill to get a strategic advantage in an upcoming battle a la Heroes of Battle?
DC examples at 5, 10, 15, 20, 25, 30, and 35?
Epic uses of the skill, using the rest of the epic skill rules as a basis?
What would the 1 or 2 minigame mechanics that would show up in a splatbook look like?
What would a weird ritual does this skill give you access to?
What would the possibly fictional stormwrack, sandstorm, frostburn, underdark, junglerash, atmospheresmertz, and Innerspace: the diminutive surgery by burly barbarians splatbooks offer the use of this skill?
What synergies are there?

I'll post a melange of the best entries, with attributions, on the guide, who knows, maybe a whole new vista of gameplay awaits the answer to the question: "what happens if I can make a DC 45 Knowledge dreams check, reliably?"

[aimlessPolymath]

Alright, let's do this (love the thread idea!)

Mechanical uses over fields of purview, which are a bit more vague:

Knowledge(Dreams): May be used to replicate the Dreamtelling (http://dnd.arkalseif.info/feats/heroes-of-horror--70/dreamtelling--759/index.html) feat, with a -5 penalty, without the feat (I judge the cost of investing in a skill with extremely limited use to be about a feat, right?)
Probably some kind of Psychology abilities, too- understand people's personality by listening to their dreams.

Knowledge(Weaponry):
Synergy bonus applied to Sunder checks against weapons.
Substitute for an Appraise check against weapons. Synergy with Appraise checks against weapons.
A DC 5 check identifies the name of a simple or martial weapon, as well as its statistics.
A DC 10 check identifies the name of an exotic weapon, as well as its statistics.
A DC 15 check discerns that a weapon is masterwork or not.
A DC 20 check discerns that a weapon is magical upon it being used to make an attack, regardless of spells used to hide its nature- you can know how it should move, and observe that it is not so.
A DC 20 check informs the user of the Craft bonus of the creature who made the weapon. (It lets you identify forgeries, notably)
A DC 25 check identifies the enhancement bonus of a weapon when it is used to make an attack, as well as properties not easily visible- enchantments such as keen, cleaving, merciful, defending, and so on may be discerned in this way.

I had fun with this one.

Knowledge(Geology):
Check can be used to identify creatures with the [earth] subtype.
Substitute for an Appraise check against gems. Synergy with Appraise checks against gems.
Synergy with Strength checks made to break rocks.
In the hypothetical book Rockslide, covering high-altitude and mountainous terrain, this skill allows people to detect unstable terrain (including whatever alternate magical terrain they come up with in that book, with type-specific DC), as well as:
A DC 20 check allows a user to identify the Climb DC of a natural surface.
A DC 15 check allows a user to identify signs that an area is rockslide-prone, automatically informing them whether a given action could set one off.
In the book Underdark, it can be used to determine location in a similar way to Knowledge(Geography).

Knowledge(Local Bars and Alehouses):
Can be used as an alternative to Gather Information.
In any settlement at least as large as a small city, this skill may be used to find safehouses with suitably discreet people. This raises the base DC of checks to perform Urban Tracking to your check result- this does not replace the bonus for "tracked party lies low".
Whenever any sort of roll is made to set up a party or engage in hedonism, you may lend your efforts, adding a +1 insight bonus to the result of that roll for every 5 points by which your check result exceeds 10. If the die being rolled is a d12 or a d20, add a +2 bonus per 5 points instead. If percentile dice are being rolled, add your check result - 10 instead. If this would bring the result over the maximum possible, it is capped by the maximum.
A DC 15 check allows the player to avoid receiving diseases as a result of partying.
(There are many types of houserules for partying, including at least one d12-and-compare-to-table that I've seen)

Knowledge(Streetwise):
Check can be made to identify the day job of creatures, Sherlock Holmes-style. A Disguise check can be used to oppose this.
Synergy bonus to Diplomacy checks made to interact with the urban lower class.
A DC 15 check can be made to deflect unwanted attention inconspicuously and safely- panhandlers are waved off, thieves see you as a hard target, gang members thing twice about mugging you, and so on.

Knowledge(Dragonkind):
Lets you identify dragons, as well as dragonborn, creatures with the dragonblood subtype, and creatures which were once dragons . Duh.
A DC 12 check lets you identify the element, breath weapon(s), and alignment of a metallic or chromatic dragon, just from hearing what color it is, except for bronze, copper, and brass dragons. (note that witness accounts can be unreliable)
A DC 14 check is required to remember which one is which between bronze, copper, and brass dragons, upon seeing them, and identify their breath weapons, elements, and alignments.
Go ahead. Tell me which has slow breath. No googling.
A DC 20 check is required to identify the immunities, breath weapon, and alignment of any other true dragon, from seeing it.
A DC 25 check allows you to identify the age category of any true dragon, from its appearance.
A DC 15 check allows you to identify the most common mistakes made by a dragon attempting to pose as a humanoid; five minutes of conversation with a one allows you to make this check to identify them as such. A dragon trained in Knowledge(local) (at least one rank) is immune to this. A DC 25 check allows you to identify the type of dragon disguising itself.

I was generally irritated that the DCs to identify dragons are so high, since they're literally color-coded. The last ability is just me amusing myself.

There's too big of a list in the link for me to pick out some, so just give me a couple and I'll work on them. I mostly went with low-DC options here, as the upper echelons of Knowledge checks are a bit hard for me to think about- Knowledge skills are rarely mechanically relevant, and once you get past "competent in the field", it's hard to think about. Once I come up with an idea, it's also hard for me to justify to myself keeping at a high DC.

[Gildedragon]

Dragonkind: identifies dragons, and dragonblood subtype creatures
DC 5 Recognize a Dragon, regardless of hit dice, as a Dragon
DC 10+RHD Identify a creature with the Dragonblood subtype. For templates use the LA or CR change (if LA -) instead of RHD. In the case of a template, you only know the properties given by the template.
DC 15 Recognize a Sorcerer with the Draconic Heritage feat, know the benefits of that feat

[JNAProductions]

Dragonkind: identifies dragons, and dragonblood subtype creatures
DC 5 Recognize a Dragon, regardless of hit dice, as a Dragon
DC 10+RHD Identify a creature with the Dragonblood subtype. For templates use the LA or CR change (if LA -) instead of RHD. In the case of a template, you only know the properties given by the template.
DC 15 Recognize a Sorcerer with the Draconic Heritage feat, know the benefits of that feat

So the average commoner (Int 10, no ranks in Knowledge skills) has a 20% chance of failing to recognize a dragon?

[Tiktakkat]

Those are all 3.0 Knowledge skills.
Which, by 3.5, are all eliminated and subsumed into the explicitly limited set of Knowledge skills presented in 3.5. (Though of course those got a bit less-limited as time went on.)
So what you actually have there are:
Knowledge: dragonkind arcana
knowledge: weaponry local or martial lore (Tome of Battle p. 28)
Knowledge: Streetwise local
knowledge: geology dungeoneering or nature (Underdark chapter 7 generally)
Knowledge: local bars and alehouses local
knowledge: dreams the planes (Heroes of Horror p. 122)

[daremetoidareyo]

This interpretation is not supported by the update booklet nor the d20 srd. Even the PHB 3.5 says "Below are listed typical fields of study. With your DM’s approval, you can invent new areas of knowledge."

[Darth Ultron]

So the average commoner (Int 10, no ranks in Knowledge skills) has a 20% chance of failing to recognize a dragon?

I do think that fits, and maybe should be higher.

I think most commoners..and people in general, will say any vague reptile or lizard like monster is a ''dragon''. And they would be wrong...of course.

The same way most will say anything that swims in the water is ''a fish'' ......

[JNAProductions]

I do think that fits, and maybe should be higher.

I think most commoners..and people in general, will say any vague reptile or lizard like monster is a ''dragon''. And they would be wrong...of course.

The same way most will say anything that swims in the water is ''a fish'' ......

That's not misidentifying something similar to a dragon as a dragon. That is seeing a literal dragon and saying "That's not a dragon".

[Jormengand]

That's not misidentifying something similar to a dragon as a dragon. That is seeing a literal dragon and saying "That's not a dragon".

I mean, why not? It's not implausible that someone who hasn't exactly done much in their life, has only lived in one place most of their life, and so forth, has never seen a dragon before, wouldn't know what one looks like.