Reaction-Roll Stealth

So far, the skill-based stealth system I've been using has been difficult to run without a battlemat, while the default "X on 1d6 to surprise" system still strikes me as pithy and undramatic (except in the simple case of encounters). But the reaction roll, which I've been using extensively through On the Non-Player Character, fits the bill perfectly - instead of binary success/failure, you get piling bonuses which slowly push you towards success or failure. Additionally, this is consistent with the current systemic division I'm contemplating - using d20s for the combat system, 2d6 for noncombat rolls, and dice pools for anything to do with magic. The following stealth system is mostly inspired by On the Non-Player character, and a bit from this Google+ discussion.

Stealth actions are resolved in segments of one minute, rolling 2d6 (plus Dex mod) each time. Bonuses are persistent, and cumulative. Consult the following table:

	Sneak	Backstab
2	Found or -4	You're surprised!
3 - 5	-2	No surprise
6 - 8	0	You surprise!
9 - 11	+2	Ranged backstab!
12	+4 or Hidden	Melee backstab!

Sneaking is used for any actions you take while undetected. The following bonuses apply:

No movement or other actions (hiding): +4
Combining two actions (moving twice, moving while tracking, etc.) -4 per action
Trickster/thief/etc. +level
Distance: +1 per 100' from nearest sentry/enemy, -1 per 10' closer than 100'
Terrain/weather/etc.: +2 or -2 depending on conditions

Found means that stealth ends (for you) and you're detected. Start encounter as normal - stealth can no longer be used. You can, of course, try to hide again - you can roll on the Sneak table instead of taking another action each round, with cumulative bonuses. Stealth starts again once you get Hidden.

Backstabbing is what you roll when you're trying to end stealth and initiate combat. On a 2, you totally bungle it, and your opponent gets to act against you in the surprise round, while on a 6 or higher, you surprise them, getting a free round. On a 9 or higher, you've spent enough time observing and positioning yourself to get a sweet sniper shot on an opponent, gaining a +4 to hit. On a 12, you're close enough to do it with a melee weapon, and can precisely target weak points or chinks in your opponent's armor - you get a +4 bonus to hit, and deal double damage.

Backstab bonuses:
Multiple actions (opening a door and then backstabbing, for example): -4 per action
Trickster/thief/etc.: +level
Distance: -1 per 100' from target, +1 per 10' closer than 100'
Terrain/weather/etc.: +2 or -2 depending on conditions

Calibrating This Shit

As Charles Taylor says, realism in the game provides a vital frame of reference for the player to be able to predict the effects of their actions, and, more importantly, put the unrealistic elements in their proper context. I'd rather have a few rules, tightly webbed and absolutely realistic, than a whole lot of quasi-fantastical and independent systems.
Finally, I have an hour and a half commute every morning, so I have little else to do but sit on the bus and consider the internal consistency of my system. So I calibrate shit.

Walking

Let's start with walking. In a combat round of six seconds, the average character can take four actions. Walking 5 feet is one action. Walking is, of course, something every player will be familiar with, so it had better work the way we expect it to.

So, you'll walk 20' in six seconds, or 200' per minute. This gets you to 5,280', a full mile, in 26.4 minutes - or about 2.3 miles per hour. This is a tad on the slow end - average human walking speed is 3 mph - but it comports with marching speed, which is a bit over 2 miles per hour over varied terrain. It's a nice, leisurely stroll - or an aware, steady advance. Realistic.

My marching speeds for unencumbered/encumbered/overencumbered people are currently 4/2/1 miles per hour, respectively - putting combat walking in the "encumbered" category. To be fair, 2 miles per hour versus 2.3 miles per hour adds up to a loss of about two and a half miles over the course of a day - but cross-country marching isn't a completely continuous slog. Internally consistent.

Running and Sprinting

Time to take it up a notch. The average human can run at 5-8 miles per hour, and sprint at around twelve to fourteen. Originally, I had running take 1d4 actions for 25' of movement, but that put "running" speed at a measly 4.5 miles per hour. I'll have to balance running speeds (1d4 actions), sprinting speeds (2d4 take lowest), and top speed (which is when every roll comes up 1).

Before we begin, I'd like to mention the rationale for a roll-to-sprint system: The uncertainty it introduces really allows me to run chases and pursuits using the combat system, pretty much unchanged, and I think it does a good job of reflecting the importance of reflexes, momentum, balance, and footing in short-distance running.

The average "run" will use up 2.5 actions, which allows for 16 runs per minute. At 40' per run, we get 640' run per minute, netting you a mile in eight minutes, fifteen seconds. This gets you 7.27 miles per hour - close to the upper average! Ideally I'd want it a bit closer to the 6 MPH mark, but it's not really a big deal.

The average of 2d4, take lowest, is 1.875 (about a 25% action cost reduction). That's 21 and 1/3 "sprints" per minute, or a 33% speed increase, for 9.7 MPH. Admittedly, this isn't a huge leap ahead of running speed, but you'll be getting top speed 80% of the time, rather than 25% of the time, which is a big advantage over short distances - exactly the balance I'd want to have.

Top speed means that you get four moves of 40', or 160' a round, 1600' per minute. That's a 3.3 minute mile! You're running at 18 miles an hour, mate. Of course, to run even a third of a mile at top speed, you'll need to roll 1 on 1d4 at least 40 times. The percentage chance of that happening on a normal run has twenty-five zeroes in it. Even while sprinting, with an 80% chance of reaching top speed each sprint, you only have a 0.0001% of getting any significant distance out of it. Which, of course, is how it should be.

The Fast Runner

You get bonus actions based on your Dexterity modifier in my system, which means a maximum of 7 actions per Round, or 75% faster movement. I'm not so concerned about the effects that a negative DEX modifier will have - crippled characters are going to be crippled, after all - but obviously we don't want a few extra points of DEX turning your character into some kind of freakish superhuman.

Which, luckily, it doesn't seem to. Walking speed, with 7 actions, is 4.03 MPH. Running speed is 12.7 MPH. Sprinting is 16.7 MPH. Pretty much all of this is in line with what I'd expect. Walking speed does tend to imply a significantly faster marching speed, but remember that long-distance marching is more an issue of endurance than speed,

Finally, the Fast Runner's top speed clocks at 31.5 MPH - faster than Usain Bolt, though not by much. This is actually a lot less realistic - modern sprinters have access to technology and training techniques that allow them to greatly increase fast-twitch muscle mass, and can thus attain significantly faster speeds than any pre-industrial sprinter. Of course, I'd rather err on the side of letting lucky player characters outstrip Usain Bolt for a few rounds, so I'll accept this quirk of the system.

Endurance

I account for fatigue and exhaustion by folding it into an encumbrance-by-stone system. Both fatigue and exhaustion are treated as a "phantom" stone of carried weight, which you can only rid yourself of by resting for a Turn or sleeping for two hours, respectively. Regular encumbrance is at 5 stones, with the max at 10 stones.

Walking (and even running) have no associated endurance or fatigue penalties, since I want each to be as simple and straightforward as possible. Over long distances, each fits easily into normal march rules, and long-distance running is easily accounted for as forced marching, which I handle by allowing the players to move into a faster march speed level than their encumbrance would normally allow, by quadrupling the rate of exhaustion.

I require sprinters to pass a STR check every sprint, or else lose any defensive bonuses and get reduced to AC6. Fumbling is possible (1 in 20 chance normally, goes up to 4 in 20 when overencumbered), which in my system usually just adds a stone of fatigue. The character can expect 21.33 sprints per minute, and 6 minutes, 11.25 seconds per mile, gaining 1.07 stones of fatigue each minute.

However, by the end of the third minute, she'll have 3 stones of fatigue and will move from "unencumbered" to "encumbered," fumbling 2 out of 10 times. (From here on out I'm going to let my precision slide a bit.) During the fourth minute of sprinting, she'll gain two stones of fatigue, making her "overencumbered" for the fifth minute. At the end of the fifth minute, she'll have gained four more stones of fatigue (fumbling 4 in 20 times!) putting her at 9 stones. This means that, fifteen seconds into the final stretch, she'll need to roll Might saves every Round to even continue sprinting - otherwise she'll be forced to the ground, resting for at least an hour and a half in order to return to zero fatigue, never having even reached the mile mark.

Someone with 18 CON (which puts base encumbrance to 8 stone) would be able to do it - she could sprint for four minutes before becoming encumbered, and would only gain her eighth stone in the sixth minute - finishing the mile on time. with enough wind for two more minutes of continuous sprinting.

I don't know that this is absolutely realistic, but there's definitely a reason why sprint races cap off at 400 meters! Anyway, a good long-distance sprint in this system would be a half-mile in about three minutes, which would require a half hour of resting to get back to tip-top shape. That sounds good enough for me.

Running a Marathon

Marathons are 26 miles, and the world records are all a few minutes under two hours - which comports with the Fast Runner's running speed of 12.7 MPH. Of course, these are extraordinary cases - marathons are better handled with marching speeds.

Most competent marathon runners aim to run a four-hour marathon, and 2% of them breach three hours. Unencumbered marching speed is 4 MPH, which is a six-and-a-half hour marathon - clearly, we have to kick it up a notch. A 6 MPH forced march - at 1 stone of exhaustion per hour - gets you across the finish line in 4 hours, 20 minutes, and an 8 MPH double-time (1 stone per turn) will be 3 hours, 15 minutes, at 7 stones. Good enough - it provides enough of a baseline to estimate exhaustion and times if someone wants to actually race in a marathon, it's easy to remember (+2 MPH when forced-marching), and it's consistent, with 6 MPH being just under running speed and 8 MPH just over.

Fighting
You can fumble in combat! Surprise surprise! You'll be rolling 10 attacks per minute, with a 1 in 20 chance of fumbling - giving you a stone of fatigue every two minutes. At six minutes, on average, you'll cross into "encumbered" territory, averaging one new stone per minute. At eight minutes, you'll be "overencumbered" and gain, on average, a stone of fatigue every 30 seconds. You'll start to collapse from exhaustion after 10 minutes, 30 seconds of continuous fighting - 105 rounds. Not having done fencing or medieval reenactment (only paintball), I couldn't tell you exactly how accurate it is, but it's on a similar scale to sprinting, and is easy to remember, and easily accommodates the effects of excess weight on your combat endurance. The idea that, after six minutes of continuous fighting, you're really starting to push your limits makes intuitive sense to me.

Sneaking
Sneaking is the skill used to move without drawing attention to yourself, and I record it in feet per minute - this being how fast you can move before making a ruckus. As a Level 1 Trickster, you get 20' per minute, going up by 20' each time you level up and decide to improve Sneaking.
20' per minute is two feet per round, or four inches per Action - the slowest flat crawl. (Although, since it's notated as a per-minute speed, it also accounts for quick dashes between cover). By Level 10, however, said Trickster can Sneak at 200' per minute, which means their normal walking is completely silent. And at level 20, she'll Sneak at 400' per minute, or about 4.6 MPH - a brisk jog!

Since you can double-time with a DEX check, you can effectively attempt to Sneak at normal speed by level 5, while a 20th-level Trickster can basically Sprint silently, with up to 800' per minute/9.2 MPH Sneaking, which is obviously pretty fantastical. This meshes perfectly with my intended level scaling, where 10th level is intended to comport with the best that heroes could have accomplished in the real world, and all the levels beyond that representing states of increasing mystical perfection. Since double-timing a skill like this adds 1d4 guaranteed stones of fatigue, it remains a poor substitute for normal sprinting when simply looking at speed.

Swimming
Base swim speed is 30' per minute, or 3' per round, increasing in those same increments. This starts you at about 0.3 MPH, whereas the fastest swimmers can reach 5-6 MPH - which, of course, comports exactly with the swim skill in my system. A 10th level Trickster fully trained in Swimming moves at 3 MPH in the water, and at 20th level she'll reach 6 MPH.

Sprinting, of course, doubles these speeds - a 10th level swimmer can sprint at similar speeds to Michael Phelps, while the 20th level will actually be a bit faster in the water than she is on land.

Climbing
I'm the least familiar with climbing techniques, so I'll use some speed climbing records as a reference point. The 2007 record (since broken) on El Capitan, a 2900 foot climb, took about 165 minutes - about 17 feet per minute on average, though the climbers were reported to do most of the climb at 20 feet per minute. Half Dome, at 2,000 feet, has been done in 82 minutes - nearly 25 feet per minute. However, the tree climbing world record is about 50' in 13.65 seconds, or a bit over 250' per minute, and the Climb skill is intended to cover both of those bases.

Of course, tree climbs are clearly sprints, moving at double time, while thousand-foot plus climbs include numerous rest breaks. We can bridge much of the gap by working backwards from my system's "skill sprint" mechanic - cutting a 250' per minute sprint in half to get a "normalized" climb speed of 125' per minute. As for the rock climbing records, we can probably assign CON scores of 18 to the climbers, which gives them the ability to simply 'take' 4 stone of fatigue before things start getting dangerous. Climbing adds 1 stone per minute, and resting removes 1 every 10 minutes. So for every 4 minutes of continuous climbing, you'd need 40 minutes of continuous resting to return to zero.

Let's apply this to the El Capitan climb. 4 minutes 'on,' then 40 off, is 44 minutes. The second stretch puts us at 88 minutes total, 8 minutes active climbing. Third, 12 minutes climbing and 132 total. A half-stretch, 14 minutes climbing and 154 total, and a quarter stretch gives us 165 total minutes, with 15 minutes of continuous climbing, at 193' per minute. As this is a world record climb, we can assume a fair amount of sprinting, as well as simply accepting extra weight, and modern climbing technology to boot. I'll call it a normal climbing speed of 100' per minute, at Level 10 - or 10' per minute, at level 1.

The "catching" mechanic (you get a chance to catch yourself while falling every 10' up to your Climbing skill distance) is definitely less realistic, as even an experienced professional climber would not be able to simply "catch a ledge" after a 50 foot fall, but it does keep things interesting and allow for additional granularity when failing to climb something.

Conclusions
Since I use an action-point system, I realize I have a level of granularity below most people's systems. However, most of this translates well, I think - see this summary of my per-Round movement speeds:
Walking: 20'
Running: 64' (or just simplify to 60')
Sprinting: 85'
Top Speed: 160'
Climbing: 1' per level
Sneaking: 2' per level
Swimming: 3' per level

Descriptive Skills

Skills in action?

To my mind, the regular kind of numeral skills are needlessly dissociated and kind of confusing. Usually, they need some sort of second-order transformation in order to be useful - so, "Climb 5" becomes "Can climb 30 feet in under a minute 75% of the time" or else "Can climb any wall any distance 83% of the time."

Instead, I'd like to notate skill levels in ways that are inherently meaningful. Here, I'm drawing from Alexis' writing about thief skills that don't suck, and Charles Angus' writing about descriptive damage.



Movement Skills

The movement skills have a base time frame of one minute - your "score" is the number of feet you can move per minute. The first minute is always successful, but every minute after that requires you to check against the linked ability score. All movement skills divide their speeds by the DR of any worn armor. (So, no penalty for leather, half speed for chain, quarter speed for plate.) You can "sprint" with any of these, moving at double speed but taking 1d4 extra stones of fatigue each time.

Climb (STR) - Climbing skill advances in intervals of ten feet. Each successful check, after the first, adds an extra stone's weight in fatigue. Failure means falling, but you can make Might checks (-1 penalty per failure, cumulative) to try to catch yourself every ten feet, until you've fallen farther than your Climbing skill.
So, if you have Climb 30', you can climb 30' free, 90' with two checks, and you get three chances to stop yourself if you fall. Falling damage is 1d10 per 10 feet, to a max of 10d10.

Swim (CON) - Swimming skill advances in intervals of thirty feet. Each successful check, after the first, adds an extra stone's weight in fatigue (and remember that waterlogged fabric can double or triple in weight). Failure means you begin to drown - roll Will checks every minute. Once you fail, you lose 1d4 INT, WIS, and CHA per minute until rescue or death. Diving uses the same mechanics, but the diving interval is 1/3 of your swimming interval, and you have to get back up!

Stalking (DEX) - Hiding, I think, is better implemented as direct player interaction with the environment and any NPCs searching for people.  Stalking is the active element - how far you can move between "hides" without drawing attention to yourself. It's judged more as a defense against being heard, or noticed out of the corner of the NPC's eye - there's no such thing as "stalking" someone by walking directly towards them in their field of vision. Stalking is like being a Weeping Angel - you can only move when they can't see you.

So: intervals of twenty feet. Stalking accrues no penalties for extended time - but the first check isn't automatically successful, and you can't "sprint." Failure doesn't immediately mean detection - rather, it means you've snapped a twig, knocked down a glass, stepped on a weak floorboard, etc. The results are, of course, dependent on the situation. Snapping a twig 100' away from a sentry might not necessarily draw any attention, but doing the same thing from 10' away will certainly get you caught. Wile saves are used to duck into cover if a guard suddenly turns around, or for simple distractions (the old rock throw, etc.)

Non-Movement Skills

The other skills are given a direct time frame, which is the time needed for automatic success. You can try to complete at half-time, rolling against the linked ability score. Each additional halving applies a -5 penalty.

Tinkering (INT) - Tinkering starts at 6 turns, and reduces by 1 turn each "skill level," until it takes 1 turn. Then it reduces by 1 minute, then by the round, etc. Therefore, three Spies of levels 6, 8, and 17, will automatically pick a lock in 1 turn, 7 minutes, and 8 rounds, respectively. If you fail the INT roll when rushing, you jam the lock.
For trapped locks, detecting and disarming the trap is its own separate task and they'll automatically activate if you don't try to find it first, but you get a Wile save to dodge its activation, in addition to the Might save to resist its poison. Failing a rushed trap detection activates the trap.

Tracking (WIS) - Tracking starts at 6 turns, reducing by the turn, then by the minute, then by the round. This is the time it takes to get a pretty good look at a patch of ground - say, 20' square, or 400' in a line (like, along a fence.). You have to re-check the track every four hours, or if it's disrupted by something like a stream, or a fallen tree, or mud. Tracks remain for about a week, by default, but again that's modified by the specifics of the situation. For things half the size of a man, you have to re-check twice as often, half that is twice as often again, etc. For things larger, the time multiplies in the opposite direction - tracking a bear means you re-check every eight hours, twice that is sixteen hours. If you rush it, and you fail, well, obviously you didn't find any traps.

Procurement (CHA) - Procurement is the process of locating things. Things like henchman recruits, uncommon items, or even information - such as rumors and gossip. Procurement doesn't include the purchase itself - though information can sometimes be had for free, or for just a few too many coppers for mead - it only covers the process of finding it. And, of course, it doesn't allow you to find things that aren't there.

Procurement starts at 56 hours - or one whole week, assuming 8 hours of work per day, and a population of about 1,000-3,000 people. Decrease the time proportionally for smaller towns, but for larger cities, the work only covers a single neighborhood. This decreases by four hours per "skill level." If you rush it, and fail, you create a bit of bad blood in town - by stepping on some toes, ignoring some customs, or going to the "wrong people." Obviously, town politics are pretty situational, but "three strikes" is probably a pretty good rule of thumb.

To determine what specialized/rare items are available, you can't go wrong with the vendor saving throw - applying, say, a -2 for items with triple-digit costs, -4 for items with quadruple-digits, and assuming anything more expensive is not going to be hanging out in some pawnshop. A successful Procurement tells you everything that's there and what it costs.

For hirelings, assuming a town of 1,000, you'll find 1d4 capable mercenaries (or other professionals) are found, and 4d6 base laborers. -1 mercenary and -4 laborers each time you halve the town size. So, a village of 250 people has 1d4-2 mercenaries and 4d6-8 laborers. Yes, there can be zero hirelings.
Rumors and secrets have to be Procured by subject, if you want anything more specific than the gossip spouted by every drunkard. Obviously, not all secrets are so easily found - since Procurement involves nothing more than asking around, crawling the pubs, and being generally alert, it will never discover information guarded with any amount of competence. The best you can get in these cases are tips to where the information might be found.

Yes, exactly, a plot hook.

Notes

A lot of other skills don't make it in - for the most part, because I think those can best be resolved with simple ability checks and some planning. Sleight of Hand counts for this (and has the added bonus of preventing people from looking at their sheet, seeing "Pickpocketing" and going $$__$$). Hunting is basically Tracking that leads to an encounter (or, like modern duck hunting, sitting on your ass until an encounter finds you).

I moved Tinkering from DEX to INT in order to support different "styles" of thievery, and because picking a lock is to my mind much more about thinking about the manner in which the lock is constructed, and how to circumvent its elements, than simply sticking your pick in the right spot.