Category Archives: Rules

Finery and social class

5 Replies
Image from Wikipedia

How people react to a character in a social situation depends heavily on how that character is dressed. Is the garb appropriate for the occasion? Does it signify similar station to that of the interlocutor? Does it show respect, or perhaps arrogance?

There are six levels of finery (seven including impoverished).

  • Impoverished (0 GP). Scavenged rags.
  • Poor (10 GP). Worn but functional.
  • Respectable (100 GP). Tradesperson.
  • Prosperous (500 GP). Official or dandy.
  • Wealthy (1000 GP). Rich merchant.
  • Noble (5000 GP). Aristocrat or hierophant.
  • Kingly (10000+ GP). The garb of emperors.

The primary benefit to wearing expensive clothes is a reaction modifier, based on your finery relative to that of any interlocutor. For example, if you are wearing poor clothes, and interacting with someone garbed in prosperous finery, the reaction roll will be at -2 (due to the two steps of difference). If you are outfitted in finery equal to your interlocutor, there are no modifiers to the social reaction role. If you are wearing clothes of a higher station, there is a bonus, but capped at +2 (the penalty is not similarly limited, however; impoverished clothing imposes a -6 reaction roll penalty when talking to a king).

Adventuring in the underworld or wilderness will quickly ruin clothes of value higher than poor unless supernatural measures are taken (some wizards are exceptionally vain and prefer impractical clothing to show their power, much the way nobles do to show their wealth). Well-crafted clothing meant to stand up the elements can be had for 50 – 100 GP, but marks one out as an explorer or scout. Fashion dictates that particularly valuable clothing must be altered and replaced with some frequency (exact replacement schedule is a function of location and referee ruling). The finery of one place may not be appropriate in another place (assume one category less, though this is also subject to situational rulings).

Ceremonial armor is also available for the prices listed above, and may be made functional as well as elaborate if desired (double the cost, you must find a master armorer, and repair costs will be high). If well maintained, standard light armor is automatically treated as poor clothing, while standard medium and heavy armor is considered respectable. However, if armor is worn in an inappropriate situation (an audience with a lord where you are not that lord’s general or mercenary, for example), it is considered to impose an additional penalty (probably -2).

First level characters and retainers begin with the equivalent of poor clothing. I don’t expect that concerns about status and clothing would come up that often for low level adventurers, but I think this nicely encapsulates social dynamics, is another way to engage the world, and could make a difference in a diplomacy-heavy domain game. This system also leverages the 2d6 reaction roll, which is my favorite RPG social resolution system.

Ghost traps

2 Replies
Sapphire image from Wikipedia

Ghost traps are items (most commonly gems) that have been enchanted to serve as prisons for spirits and incorporeal undead. Clerics of any level may create ghost traps with hit dice capacity no greater than their level. Ghost traps may contain no more than one spirit, even if the trapped spirit has hit dice less than the capacity of the trap. When occupied, a miniature version of the spirit can be seen leering within the gem, seemingly contorted and tormented.

To create a ghost trap, a cleric must have a gem of value equal to the desired hit dice capacity multiplied by 100 GP. For example, a 3 HD ghost trap requires a 300 GP gem. In addition, hit dice capacity * 100 GP must be spent on ritual components, and the whole process takes 1 week. There are some situations described below where a ghost trap is destroyed. In these cases, the gem crumbles to ash.

To use a ghost-trap, it must be strongly presented within 10′ of the spirit (this is a standard combat action). If the spirit fails its saving throw versus magic, it is imprisoned in the gem. A trap may also be thrown, but if the spirit makes its saving throw, there is a 1 in 6 chance that the gem will be destroyed when it hits the ground. Turned spirits do not get a saving throw and may be automatically imprisoned. All classes may use ghost traps, though clerics may set them as traps that will trigger when spirits draw near. An attempt to trap a spirit more powerful than the capacity of a given trap will automatically fail, and there is a 1 in 6 chance that the trap will be destroyed.

Trapped spirits may be released at any time, though they will generally be quite unhappy about having been imprisoned (-2 reaction). Releasing a spirit has a 1 in 6 chance of destroying the trap (otherwise it may be used again). Trapped spirits may speak telepathically with anyone touching the gem directly, will generally beseech any holder for freedom, and may promise all sorts of rewards (probably all lies). This contact is one-way, however, and it is impossible to communicate with a trapped spirit without using magic (see the magic-user ritual below).

Though only clerics can create ghost traps, many magic-users prize occupied ghost traps, as they believe that they are valuable currency in the land of the dead, and can also be used in arcane researches. Magic-users can also conduct rituals to communicate with trapped spirits. This requires 1d6 * 100 GP worth of components, and requires a saving throw versus spells. On a saving throw roll of 1, the spirit is released (or some other suitable magical mishap occurs). If the magic-user succeeds on the saving throw, the spirit will answer 1d6 yes/no questions to the best of its ability, and will be unable to lie.

(Though I know about Skyrim soul gems, the inspiration here is more Ghostbusters.)

(In Hexagram, the ability to create ghost traps comes with the banishment trait.)

Lamentations of the monk

4 Replies
Quick sketch by Gus L. during play

Yesterday I ran a high-level (8 + 1d4) LotFP adventure play test. One of my players wanted to play a monk-type character that specialized in unarmed combat. To support that, I bolted on some of the AD&D monk powers to the LotFP fighter, and specified that the attack bonus would only be available with unarmed strikes.

These are the capabilities that the 10th level monk-fighter ended up with:

  • 2d6 + 1 open hand damage
  • 2 attacks per round
  • Self-heal 1/day 1d4 + 4 HP (takes one turn)
  • Wuxia jump (10′ vertical)
  • Saving throw to punch mundane missiles out of the air

The 2 attacks + high damage might seem like a lot in a LotFP context (and it is), but striking something with your hand opens you up to certain dangers that I would certainly run with (for example, punching something with acidic skin).

It worked out well, and I would use it again. Possible changes and additions:

  • Improve the self-heal, to 1d4 + level available from level 1.
  • Wuxia jump would also probably be 10′ + 1′ per level.
  • An ability for running up walls patterned after the specialist’s climb skill.
  • Rather than make two attacks, the monk could attempt a single stunning strike which would paralyze a humanoid target on a failed saving throw (recovery on 1 in 6, checked per round).

I gave no AC bonus and would not change that. Monks can wear armor if they want to, with appropriate penalties. The unarmed strike damage would be lower at the beginning and progress with level.

Postscript: rolling for appearance randomly is fantastic. The player opted to do that and the character ended up as: Mature Male, Immaculate, Obese. How many PCs do you often see like that?

Using Attack Ranks Defensively

5 Replies
Battle of Castillon (source)

In the ratling post, I alluded to an ability to use attack ranks for things other than just an increased chance to hit. Specifically, ratlings can use attack ranks to improve their armor class on a round by round basis, with each rank so applied improving the effective AC by one armor category. Ratlings naturally have light armor (AC 7). For example, a ratling who fights at attack rank 1 may choose each round whether she wants to have AC 7 and attack rank 1, or AC 5 and attack rank 0.

Fighters (but no other class) may also use attack ranks defensively in a similar way to improve their AC from round to round. In addition, fighters may spend their attack ranks to improve the AC of companions they are defending if that makes sense situationally. For example, consider a first level fighter wearing medium armor, using a shield, and fighting near an unarmored magic-user. This fighter has AC 4, the magic-user has AC 9. The fighter has the following options:

  1. Fight at attack rank 2. All armor classes remain unmodified.
  2. Fight at attack rank 1 and improve her own armor category one step (AC 2).
  3. Fight at attack rank 1 and improve the magic-user’s armor category one step (AC 7).
  4. Fight at attack rank 0 and improve the magic-user’s armor category two steps (AC 5).

Armor class may never be improved beyond AC 2. Defensive assistance from multiple fighters does not stack. Defensive assistance may be divided between multiple companions if that makes sense. I am not sure whether or not this floating defensive bonus should stack with armor. For now it does (as I would like to see people use this option some of the time). Fighter retainers may be instructed to defend their employer. Fighters must be armed with melee weapons or shields when defending companions (not missile weapons).

This ability is similar to the defense trait from the Hexagram path of arms. I think it is a nice addition to the fighter class, giving them some ability to defend other characters mechanically without resorting to other cumbersome subsystems. I could also imagine attack ranks potentially being usable for other things too, though I don’t want to overload the system too much.

Adjusted Attack Ranks

3 Replies
Battle from Holkham Bible (source)

The OD&D alternative combat system implies the use of attack ranks (discussed here and here previously). Based on my experience running Pahvelorn so far, I would like to adjust slightly how the various classes interact with this system.

Like armor, there are four categories of combat focus; each one corresponds to one of the four core classes. In the table below, focus is how much effort the class spends on improving combat skill. Begin is what attack rank members of the class have at level one. Improvement is a list of the levels where the class gains an attack rank. Max is the maximum attack rank attainable by members of the class. Regarding the maximum, keep in mind that no creature ever has AC less than 2 in this game.

Combat Competency By Class
Focus Class Begin Improvement Max
None
magic-user
0
none
0
Light
thief
1
5, 9
2
Medium
cleric
1
5, 9, 13
4
Heavy
fighter
2
4, 7, 10, 13
6

(Edit: starting thief attack rank changed from 0 to 1.)

The various classes are balanced around these trade-offs. For example, a magic-user is assumed to spend their time studying the stars and experimenting with new magic formulae. If they instead spend their time drilling and practicing skill at arms, their magic will suffer. Such things will be handled on a case by case basis within the game, and come with special requirements, such as finding a teacher.

Attack Rank
AC 0 1 2 3 4 5 6
2 18 16 14 12 10 8 6
3 17 15 13 11 9 7 5
4 16 14 12 10 8 6 4
5 15 13 11 9 7 5 3
6 14 12 10 8 6 4 2
7 13 11 9 7 5 3 2
8 12 10 8 6 4 2 2
9 11 9 7 5 3 2 2

Some further notes. Magic-user combat skill has obviously been pared down. Max thief combat skill is also capped lower, but note that a surprise attack allows the thief to attack as if with two extra attack ranks (that’s the translation of +4 to attack). The matrix has also been adjusted to reflect that a 1 is always a miss.

Attack rank attained will also affect what enchanted weapons a character can master (that is, use with full potential). This is an idea that I have been playing around with in Hexagram, and I believe it fits here as well, and is a more elegant solution than than just restricting weapons by class.

Random appearance table

10 Replies

The LL supplement Theorems & Thaumaturgy (my review can be found here) contains a magic item called ring of appearance warping. When worn, the wearer’s appearance changes randomly every turn. A useful table is included to help determine the appearance shifts. Further, the table is of the “roll all the dice” form (well, 4 of the 6 dice, but close enough). This makes it very easy to use without needing to roll multiple times.

It seems to me like this table would be very convenient for use as a random appearance generator for both PCs and NPCs. As it is open game content, I can reproduce it here for general use (and this post should be considered open game content). Thanks to Gavin for giving this to the community.

Die Result d4
Sex		 d6
Age		 d8
Dress		 d10
Features
1
 Female Child Messy Missing limb
2
 Female Youth Scant Obese
3
 Male Adult Immaculate Scrawny
4
 Male Mature Formal Muscular
5
 Old Threadbare Bald
6
 Decrepit Elaborate Hairy
7
 Drab Tall
8
 Uniform Short
9
 Ugly
10
 Beautiful

Here are a few other decent tables that I know about:

  • Gygax DMG NPC personae section (page 100 – 102)
  • Labyrinth Lord AEC tavern patron traits (page 150)
  • LotFP Grindhouse Referee Book NPC characteristics table (back cover)
  • Pathfinder GameMastery Guide NPC Creator’s Toolbox (page 94)

Am I missing any other good ones?

My NPCs tend towards blandness and similarity, so I think I should make more use of resources like these.

Ratlings in Pahvelorn

18 Replies
Rackham (source)

Rackham (source)

Or, how I discoverned what halflings were like in my setting.

The sequence of events was as follows.

  1. Gustie’s first PC, a fighter named Lune, was incinerated by a fire-breathing statue trap.
  2. For his next character, he decided to create a thief, Beni Profane, a rat-catcher.
  3. After an adventure, Beni went carousing and failed his saving throw. He rolled a 19, which is: When in a drunken stupor you asked your god(s) to get you out of some stupid mess. Turns out they heard you! Now as repayment for saving your sorry ass, you’re under the effects of a quest spell.
  4. I asked Gustie what god or spirit Beni worshipped, to which he responded none. So I asked him what god he feared, and he came back with The Mother of Thousands, a six-armed rat spirit.
  5. And so was Beni was given a quest in his dreams by The Mother of Thousands.
  6. The problem, as it turned out, was that a group of ratlings was being persecuted by the Priest-King Agamos, lord of the stronghold of Ilum Zugot to the northwest (map).
  7. The ratlings had recently taken over some abandoned grave barrows as shelter, and were stealing grain from the Priest-King’s farmers and grain stores.
  8. The PCs successfully negotiated a deal between the rat-folk and the Priest-King where Agamos would give them grain in exchange for direction to more sealed barrows and spying on those around the Priest-King’s domain (especially Efulziton the Unseen, a necromancer to the south).

Ratling Class

  • 2d6 for strength and constitution
  • Level progression as thief
  • Hit dice as magic-user
  • Attack progression as cleric
  • No skill with armor, but see below
  • Only small weapons may be used without penalty
  • Weapon damage is “two dice, take least” or one die if wielded with two paws
  • May use their bite to attack (1-3 damage) or chew through things like ropes
  • Climb Walls, Hear Noise, Hide in Shadows, Move Silently, Pickpocket
  • Smell-based search rolls (including detecting poison) as Hear Noise
  • Natural AC as light armor (leather)
  • Round to round, attack ranks may be used to improve AC
  • +4 save versus wands, dragon breath, and disease
  • May speak to rats and related rodents (only general concepts)
  • Can squeeze through extremely small openings
  • For starting retainer roll d6: 1-3 giant rat, 4-6 young ratling

Ratlings detest most domesticated animals, but sometimes have giant rats (HD 1-1, AC 7, damage 1-3) as companions. Humans also will generally not follow them as retainers. Thus rather than a standard retainer, ratlings may begin with a giant rat or ratling youth. It is common for young ratlings to be taken on short tours of the world at large, to teach them how to hide from civilized folk and familiarize them with all the dangers that threaten rat-folk. Most return to their burrows terrified of everything, but a few rare ratlings acquire a taste for adventuring.

Ratling youth

HD 1-1, AC 7, bite, smell, and climb walls as above; convert to full ratling at 100 XP.

Another encumbrance system

20 Replies

Image from Wikipedia

Back in March, Papers & Pencils posted a point based encumbrance system. It is similar to the LotFP slot-based encumbrance system and the less abstract encumbrance by stone system, but it bases how much you can carry on your strength score.

Encumbrance is measured relative to strength points, with most items being worth one point of strength (insignificant items do not count at all, and bulky items cost two strength points). An encumbrance of less than or equal to the strength score is considered unencumbered, with greater encumbrance being calculated by multiples of strength. So, for example, a character with strength 12 who was carrying 17 encumbrance points worth of equipment would be considered lightly encumbered. Each tier has associated penalties like you might expect (decreased speed, penalties to physical actions).

It’s a good system. Like the LotFP way of doing things, it’s a huge improvement over counting exact poundages (Third Edition) or coin-equivalent weights (TSR editions of D&D). However, I feel like it still requires a decent amount of calculation overhead, and this is especially difficult to coordinate for games played by videoconference (which is where I am doing most of my gaming these days). There have been a number of other blog posts about more visual slot based systems where players essentially fill out worksheets. I also feel like those are too much work to be easily adopted and maintained.

My current OD&D game is “officially” using this backpack-based encumbrance system I drafted back in July, but in practice it’s been more of a “keep it reasonable” kind of thing. The party as a whole does move slower since some of the PCs are wearing plate (and party speed is determined by the slowest members). It would be important if someone was in a drowning situation. But honestly, I don’t feel like it has made much difference.

The problem, I think, is that the movement penalty is not salient where movement happens entirely in a shared imaginary space. Ultimately, there are really two things that an encumbrance system should accomplish, in my opinion. The first is a sense of verisimilitude and realism (that’s right, I just used two trigger words). The second is that encumbrance should make choices of what to bring an interesting trade-off. In a perfect world, I would like the fighter’s choice of what weapon to bring along to be just as interesting as the magic-user’s choice of what spell to prepare.

So here is my super simple proposal, inspired by the Papers & Pencils strength based system. Items are categorized as either significant (sword, dagger, scroll) or insignificant (fishhook, ring, coin). Characters can carry a number of significant items equal to their strength score with no penalties, and up to 100 insignificant items (I don’t expect that anyone would actually want to carry that many insignificant items, but it obviously can’t be truly unlimited). For every extra significant item carried, characters take a -1 penalty to all physical rolls. So, for example, 3 extra items results in a -3 penalty to attack rolls, saves, etc.

That may sound harsh, but the more I think about it, the more I am convinced that it is actually realistic. An unencumbered person is able to fight just as well and move just as quickly as a person who is carrying nothing at all (that’s literally what being unencumbered means according to the system). In my past job, during my commute I would usually be carrying a briefcase with a few items inside and a canvas bag with two lunches and 1.5 liters of water. I’m relatively in shape, and I felt encumbered. I’ve also been backpacking, and even if modern equipment is used and items are packed well, it’s still quite awkward and tiring. Verisimilitude is less important to me than a functional game system, but in this case I think both requirements are satisfied.

Having extra items in a backpack or sack that is easily dropped for combat is one way of avoiding some penalties while still carrying more gear, but note that saving throws made during standard exploration will be penalized by the extra encumbrance. Further, if you drop your backpack during combat and need to retreat, that backpack is getting left behind for the enemy.

The thing that I like about this is that the -1 penalty per extra item makes “just one more item” have immediate consequences. In most of the other systems I have seen, it is possible to add another sword and stay within lightly encumbered or whatever. I think that kind of structure fights against both a sense of immersion and meaningful choices.

Examples of encumbering items:

  • Sword
  • Shield
  • Torch
  • Wand
  • Suit of armor
  • Quiver of arrows
  • Staff
  • Dagger
  • Scroll
  • Book
  • Potion
  • Thieves’ tools
Examples of insignificant items:
  • Basic clothing worn
  • Pendant
  • Gem
  • Ring
  • Holy symbol
  • Belt pouch
  • Fishhook
  • Flint & steel
  • Coin

Rules of thumb:

  1. If the item has system weight (and is not a magic item), it is probably encumbering.
  2. If it is a magic item that can be crafted without extraordinary requirements (scrolls, maybe potions), then it is encumbering.
  3. Items made for helping to carry other things are insignificant in moderation (backpacks, belt pouches).

Silvered weapons

15 Replies
Image from Wikipedia

Some foes, such as lycanthropes and wights, are immune to standard weapons but vulnerable to silver, and most or all versions of D&D include silver versions of various items in the equipment list. OD&D prices silver arrows at 5 GP per arrow (compared to a quiver of 20 arrows for 10 GP), and Moldvay prices silver daggers at 30 GP (ten times as much as the standard dagger). Silver crosses are also available for 25 GP (the simple wooden variety is only 2 GP).

However, treasure hunting adventurers are not very price sensitive regarding mundane equipment, so increased cost does not have much effect other than during initial equipment buying. Thus, there should be some trade-off to using a silvered weapon other than just costing more initially. Otherwise, players will just outfit everyone with silver versions of everything, and then combattants will be assumed to always use silvered weapons, just in case. Most things that are unproblematically better are boring. So there should be some reason to not use silver weapons all the time.

A silvered weapon is not actually made of solid silver. Rather, it is an iron or steel implement that has silver bound to the blade in a process similar to gilding. Perhaps a ritual and some hedge magic or blessing is also required as part of the procedure. As it is used, the silver wears off. This process of wearing off is actually critical to the effective functioning of the silver weapon — you are essentially leaving traces of poison in the argyrophobic  creature.

A “silver die” (d6) should be rolled along with every damage die. On a silver die roll of 1, the silvering process has worn off, and must be re-silvered. Needing to roll an extra die also draws attention to the use of a silver weapon, making it more of an explicit choice, and less of a default. This makes silver arrows potentially more cost-effective than most silvered melee weapons (though note you can’t effectively fight with a ranged weapon if you are in melee). Also, a miss with a silvered melee weapon will not potentially degrade the weapon, but an arrow that misses may be damaged or lost. So the value comparison is not direct.

Most metal weapons can be silvered. The cost (following Moldvay) is ten times the normal weapon, and takes a skilled smith one week to complete. Given the cost of silvering, it makes sense to only use silver weapons when they are likely to make a difference. This is in effect a form of melee ammunition.

Silvered plate armor is available too, at the same cost multiple. Argyrophobic foes will generally prioritize attacking characters that are not wearing silvered armor, and will usually take a penalty when attacking combattants armored in silver (though this varies based on the specific creature). Silvered armor will also wear out in a similar manner (a silver die should be rolled per attack that is landed on the wearer).

Thief skills

2 Replies
Cropped image from Wikipedia

Eric recently did a clarification post on thief skills for use with B/X D&D, based on the idea of leaving the basic percentages as is (that is, working with the basics of the traditional system without completely rewriting it). The thief class in my Pahvelorn game is a version of the Greyhawk thief, modified slightly to fit the mechanics of the 3 LBBs. My general approach is similar to Eric’s, though I have not committed to writing how the skills are resolved (despite much rumination on the thief class in general). Here is an attempt at guidelines for thief skill use.

Thief skills include Climb Walls, Hear Noise, Hide in Shadows, Move Silently, Open Locks, Pickpocket, and Remove Traps. All of these are percentile skills, other than Hear Noise.

The following general principles apply to all percentile thief skills.

  1. Failing with a roll of 96, 97, 98, 99, or 00 means something goes wrong. The thief falls, the trap goes off, the lockpick breaks. Depending on the circumstances, the consequences of something going wrong may be dire (though a further saving throw might apply).
  2. Failing with a roll of 95 or less means the thief makes no progress, but does not suffer any other negative effects. Another attempt may be made. Most attempts take one turn, but see below.
  3. Succeeding by more than half means the skill use is quick. For example, if a thief has a 30% chance of success and rolls a 15 or less, the task was accomplished with alacrity. The exact amount of time required is up to the referee, but it should take much less than a full turn.

Move Silently is an attempt to approach or move past an enemy without being detected. Any action taken while moving silently automatically gains surprise.

Hide in Shadows allows a character to remain hidden even if someone is searching. Any action taken while hidden in shadows automatically gains surprise.

Regarding the two stealth skills, as specified above in principle 2, failing a Move Silently or Hide in Shadows roll does not mean that they are noticed (unless the roll is particularly bad, as laid out in principle 1). Neither Move Silently nor Hide in Shadows may be used in combat.

Characters other than thieves (or thieves that fail a stealth-related skill check) still have recourse to the standard chance of gaining surprise. This is 2 in 6 by default per encounter. It may be adjusted up or down based on the specific situation and character preparation.

Picking locks and removing small mechanical traps require tools and the special training of the thief. Larger traps must be disabled or avoided by player ingenuity. Traps may be discovered by using the same procedure for secret doors: 1 in 6 chance per turn (2 in 6 for demi-humans) given a 10′ x 10′ area, or by engagement with clues and explicit description.

Hear Noise functions exactly as the standard 1 in 6 listen at doors action, but with better chances.

Armor penalties apply to all percentile skills and are -20% if wearing chain and -30% if wearing plate. Hear Noise may not be attempted if wearing a helm.

I think this also reveals an interesting potential taxonomy. Listening and searching (the d6 checks) have to do with the state of the environment external to the thief. Whether or not a trap is present or a monster is beyond the door is not a function of the character. It’s either there or not. In contrast, all the other skills represent something about the character. Climbing, picking locks, removing traps, etc — these are all things that the character in some sense controls (particular task difficulty notwithstanding). Further, they are things that a character experientially can perceive the success of. They know whether they have failed to make progress climbing the wall or have fallen in a way that is different than a failure when attempting to use Hear Noise. Is there nothing there or did I just not hear it? This also explains why there is a Remove Traps percentage, but no Find Traps, as that is covered under the search action.

Thus, I propose the following final generalization: the d6 checks are rolled by the referee (to represent the objectivity and externality of the environment) and the percentile checks are rolled by the player. Even the Hide in Shadows and Move Silently skills, if looked at in the proper light, are not about being perceived by others, they are about the thief’s talent. Why shouldn’t the thief know whether or not they have successfully hidden in shadows? Thus, the thief can use the skill before they need to depend on it, unlike the surprise roll, which always happens when the thief is already potentially face to face with danger.

Note that this approach is more forgiving in several ways than the guidelines in Supplement I: Greyhawk, which specify (page 5):

The ability of a thief to climb is also a function of his level. There is a basic chance of 13% that a 1st level thief will slip and fall in climbing. With each higher level attained by the thief this chance is reduced by 1%, so that a 10th level thief has but a 4% chance of slipping.

And, regarding Open Locks, Remove Traps, Pickpocket, Move Silently, and Hide in Shadows (page 11):

A score above the indicated percentage means failure, and no further attempts may be made.