Momentum in 2d20 is generated when you roll more successes on an action test than required by the difficulty of the check. These points of Momentum can be spent to either immediately improve the result of the current check or saved to be used in the future, allowing you to build Momentum over the course of several lesser actions until you can accomplish big things.

Momentum can be spent to do stuff like:

• Add +1d20 to future skill tests
• Create obstacles for opponents (generally increasing the difficulty of their skill tests)
• Improve the quality of success
• Increase the scope of success
• Reduce the time required to accomplish a task
• Perform a normally noisy action stealthily
• Take an extra action in an action scene
• Boost damage on an attack
• Get a called shot
• Trigger program effects in Infowar

And so forth.

In Infinity we also specifically emphasized that Momentum is best seen as a creative tool for empowering the players. The GM is also given several structures for making complex rulings around Momentum (see p. 407 of the core rulebook).

One of these is using Momentum to model preparation. If the PCs want to take one action to set up or create advantage on another, the GM can call for a test on the first action (even if it normally wouldn’t require an action test) and then any Momentum generated on that test represents the advantage gained on the primary task.

One of the limitations to this approach, however, is that Momentum ablates over time. At the end of each scene, the team’s pool of saved Momentum is decreased by one. This means that if you want to set up an advantage in one scene that will benefit you for the next scene, it’s difficult to do that.

This problem can be solved by adapting a cool mechanic from Trail of Cthulhu: dedicated pools.

DEDICATED MOMENTUM POOLS

A dedicated Momentum pool can only be used in a given circumstance or in relation to a given subject. For example, you might hack the security cameras in a megacorp’s headquarters, creating a pool of Momentum that can be spent on things like Stealth and Observation tests when the PCs go to infiltrate the HQ.

GMs might also rule that certain resources simply grant a pool of dedicated Momentum. (Perhaps the patron who hired the PCs to steal the megacorp’s new research into captured Tohaa technology simply hands them the access codes to the security cameras as part of their briefing packet. They get the same dedicated Momentum pool even though they didn’t make any skill tests to obtain it.)

There are two advantages to a dedicated Momentum pool.

First, the dedicated Momentum pool does not ablate. The dedicated Momentum pool is separate from other saved Momentum and does not decrease at the end of each scene. This makes a dedicated Momentum pool a great model for preparations that play out over multiple scenes or which are made long before their intended use: The PCs lose some of the utility of the Momentum (since it has to be used for a specific purpose), but in exchange the Momentum becomes more durable.

Second, the dedicated Momentum pool can also create unique vectors that allow the PCs to take actions that they otherwise couldn’t. If you have access to the security feeds, for example, you can check them for activity in other areas of the building. If you have a copy of the religious text of an extremist Morat cult, you can reference it for information about their rituals that you would otherwise have no way of knowing.

These vectors can cut both ways, though! When the Momentum from the security camera pool runs out for example, it could easily justify the GM spending Heat to generate a complication in the form of the megacorp’s hackers realizing their system has been compromised and launching an Infowar attack on the PCs.

Trail of Cthulhu contains some rudimentary guidelines for the use of explosives. They can be found on my system cheat cheet, but I’ll briefly summarize them here for easy reference.

SETTING EXPLOSIVE DEVICES: Requires an Explosives test. A Sense Trouble test (difficulty 4 or the result of the Explosives test) can be made to dive out of the way our pull comrade to Close range.

THROWN EXPLOSIVE: Make an Athletics test (difficulty 2 for point blank range, 3 for close range, or 5 for near). If aiming for for a very specific spot the difficultyies are 3 for point-blank, 4 for close, or 7 for near. If the explosive is not balanced for throwing, add +1 difficulty.

OTHER EXPLOSIVES: Artillery/mortars use a Mechanical Repair test. Rifle-Grenade uses a Firearms test.

TRANSPORTING EXPLOSIVES

These basic guidelines are quite useful. However, at the, let’s say, “prompting” of my players, I’ve found the not-so-occasional need to figure out what might be involved in the transportation and use of truly prodigious amounts of explosives. In the case of globetrotting campaigns like Eternal Lies or Masks of Nyarlathotep, this has often included hauling explosives on lengthy wilderness expeditions. (You’ll probably have similar experiences with the scenarios in Pelgrane’s Mythos Expeditions, although I don’t own that book personally yet.)

DEDICATED PORTER: An additional porter is required per 1 large gun or 1-3 charges of dynamite.

CARRIED BY INVESTIGATOR: If explosives are carried by an Investigator, they will suffer damage per day and an increased difficulty to physical tasks (as shown on the table below). A maximum of 6 charges can be carried by a single Investigator.

URBAN AREAS: Transporting large amounts of explosives through metropolitan regions usually requires a Stealth test (or similar precautions). The difficulty of this test is increased based on the number of charges (as indicated on the table below).

When running a globetrotting historical Trail of Cthulhu game — whether set in the 1890’s, the 1920’s, or the 1930’s — it’s not unusual for the investigators to find themselves trekking out into the wilderness, akin to those expeditions described by H.P. Lovecraft in The Shadow Out of Time or At the Mountains of Madness.

Pelgrane Press has actually published an entire collection of such scenarios in Mythos Expeditions, which I understand to also include a rather robust set of rules for organizing and running such expeditions. I’m afraid I don’t actually own that particular volume, and the rules you’ll find here are unrelated to whatever full-fledged mechanics you might find there. What I wanted/needed was a relatively streamlined set of mechanics that could be used to meaningfully organize expeditions as part of a larger campaign in which they were not necessarily the primary focus, but nevertheless a significant part.

EXPEDITIONS

These guidelines assume a modest, personal expedition consisting of a fairly typical group of investigators, perhaps one or two local guides, and their porters. They’re not appropriate for larger groups, industrial-scale explorations, or military expeditions into the wilderness (although adapting them to such might not require too much effort).

SUPPLIES: The supplies for an expedition require a 1-point Credit Rating spend per week of supplies.

PORTERS: The expedition requires 1 porter per investigator, plus 1 porter per guide. It generally costs a 1-point Credit Rating spend per porter, but Bargain reduces the total cost by 1-point. A 1-point Bargain spend halves the total Credit Rating cost for porters.

If an expedition will last for more than three weeks, the number of porters must be doubled (due to the increased number of supplies to be carried).

GUIDES

In broad terms, a guide will provide a pool of Outdoorsman points (and other expertise which may or may not be useful). In certain circumstances, guides may also possess specific navigational knowledge (i.e., the location of a “lost” locale or local watering holes) or other advantages (friendship with local, usually hostile tribes).

TRACKLESS WASTE: Navigating through a trackless waste is not trivial. It requires a 1-point Outdoorsman spend simply to navigate out of the waste. (For example, getting to the Atlantic coast from the midst of the Amazonian jungle.) Getting to a specific point of your choosing is a 2-point Outdoorsman spend.

However, a map or compass each counts as a 1-point Outdoorsman spend. (So if you have the Outdoorsman skill, a map, and a compass, you can get to a specific point of your choosing without any spend.)

FINDING A “LOST” LOCALE: Sometimes you don’t actually know the specific point at which you can find whatever it is you’re looking for. (For example, you might be searching for the lost city of Irem.) For each week of the expedition, the expedition rolls 1d6. Assuming the location actually exists and is in the region they’re searching for it, they’ll find it if the die rolls “6”.

The Investigators and their guides can spend points to enhance the search. For every 3 points spent, they can roll an additional d6. Such spends could come from Outdoorsman, Archaeology (analyzing ruins throughout the area), Anthropology, Oral History (questioning locals), or any other skill for which a logical purpose can be proposed. (This will be highly dependent on the particular circumstances of the specific locale being searched.)

INTERPRETERS

Whether on an expedition or not, any Investigator without an interpreter who cannot speak local languages must make 1-point spends with Interpersonal abilities that would otherwise function without a spend. Acquiring an interpreter generally requires Bargain or Streetwise.

Acquiring an interpreter without Assess Honesty may result in hiring an unreliable fellow. Such an interpreter may do something that could inconvenience or even harm their employer (abandoning them, stealing from them, warning local cultists, etc.).

OTHER CONCERNS

Depending on where the expedition is located, it may be appropriate to use a Heat track (or similar environmental impact mechanic). Investigators who insist on hauling large quantities of explosives into the outback will find themselves saddled with additional logistical concerns.

Not quite as auspicious as Gary Gygax’s house rules, but these are the house rules we’ve developed as part of my Thracian Hexcrawl open table campaign.

Virtually all of these rules are the result of discussing the rambling inconsistencies of the rulebooks. For the first five or six sessions of the campaign, in fact, every session started by tackling a few key passages and trying to unravel their meaning (which led to many different experimentations). Over time, however, the table settled sort of naturally into a set of “standard practices”, at which point I codified them and printed up a small booklet to accompany the copies of Volume 1: Men & Magic I have on the table.

WEAPON DAMAGE

One-Handed Weapons: 1d6
Two-Handed Weapons: 2d6, take highest
Light Weapons: 2d6, take lowest

Bows
Short Bow: 2d6, take lowest
Long Bow: 1d6
Composite Bow: 2d6, take highest

Crossbows
Light Crossbow: 1d6
Heavy Crossbow: 2d6, take highest

(In OD&D, despite a lengthy list of different weapons all costing varying amounts of money, all attacks do 1d6 points of damage regardless of what weapon you’re using. This always prompted merry discussion. It gave rise to a memorable session in which a character opted, instead of buying a proper weapon, to simply turn 1 gp into 100 cp and then hurl copper pieces for the duration of the session. During this time period I read James Maliszewski’s Dwimmermount Campaign House Rules and mentioned his rule for two-handed weapons (2d6, keep highest). Everyone liked it and we quickly expanded upon the concept.)

DUAL-WIELDING

Dual-wielding grants you a +1 bonus on your attack roll. On a hit, you deal damage as per the most effective weapon. (You can’t dual-wield with a two-handed weapons unless you have more than two hands.)

HELMETS

Not wearing a helmet inflicts a -1 penalty to Armor Class.

(This was another rule prompted by consideration of the equipment list: Helmets are listed, but what are they good for?)

SHIELDS

Shields grant a +1 bonus to Armor Class (as shown on the combat tables) when they are readied. (Surprised characters do not benefit from their shields.) In addition:

Shields Shall Be Splintered:Whenever you take damage, you can opt to have the damage absorbed by your shield. The shield is splintered and destroyed, but you don’t take any damage from the blow.

Magic Shields: You can do the same with a magic shield, but the shield won’t be destroyed. Instead there will be a 75% chance that the shield will lose +1 of its enchantment.

Magic Shields vs.  Spells: In addition, you can automatically sacrifice +1 from a magic shield in order to make a successful save vs. any spell, breath weapon, gaze, or similar effect.

Special Materials:

• Dragonscale Shields: Can be sacrificed like a magic shield in order to make a successful save vs. any spell, breath weapon, gaze, or similar effect.
• Silver–Faced Shield: Functions as a magic shield against spectral attacks (75% chance of the silver-facing being ruined).

(These rules are adapted from Trollsmyth’s Shields Shall Be Splintered and Aeons ‘n Auguries’ Splintering Shields by Material. Unlike the other house rules here, I included these simply because I liked ’em so much. The result? Unlike the other house rules, these are basically never used.

What I like about all of these house rules, however, is that they provide a simple-yet-effective method of making greatsword wielders (effectively +1 damage), dual-wielders (+1 to hit), and sword-and-boarders (+1 AC plus the splintering) all mechanically diverse and rewarding options.)

MOVE/TURN IN THE UNDERWORLD

1 turn = 10 minutes = 10 rounds = 2 moves
1 segment = 5 minutes = 1 move

1 move = speed x 10 feet
1 turn = 2 moves = speed x 20 feet
1 turn of flight = speed x 40 feet

Search a 10’ wall = 1 full turn
Listening/ESP/Clairvoyance/X-Ray = 1 quarter turn

(Check out Reactions to OD&D: Turns, Rounds, and Segments – Oh My! for a complete description of archaeological text work that was required to piece out this system.)

COMBAT SEQUENCE

• Declare Magic / Preparations
• Missiles
• Movement
• Magic
• Movement
• Melee
• Miscellaneous

All actions in a phase are considered simultaneous. If a character becomes incapacitated in a phase, they will generally not deal damage in that phase.

Surprise: Surprise allows one movement and one action.

Magic: Includes turning and most magic item use. Characters preparing to cast cannot take other actions. Any damage suffered while preparing forces a prime requisite check (modified by damage taken) to avoid losing the spell / turning.

Preparations: Retrieve 1 item, stow a weapon, draw a weapon (while dropping current weapon), pouring oil in front of you.

Missiles: Firing into melee has 50% chance of hitting a random target.

Movement: Move a number of feet equal to your speed (6” = 6 feet) or charge at twice that rate (suffering -2 penalty to AC and attacks for round).

Melee: If you’re engaged in melee, all non-melee actions (spells, missile fire, etc.) are considered a miscellaneous action and delayed until that phase. You cannot attack during melee if you are waiting to take a delayed action in the miscellaneous phase. (A spellcaster forced into melee during the first movement phase can’t cast until the miscellaneous phase, even though they were out of melee when they declared their spell.)

Miscellaneous: Includes helping wounded comrades, imbibing potions, lighting a flask of oil, etc.

Note: It is possible to shoot a missile weapon, move, move again (into melee), make a melee attack, and then drink a potion (although this would require you to be wielding a one-handed missile weapon and a one-handed melee weapon, since you wouldn’t be able to switch weapons between those actions). Similarly, one can declare a spell, cast a spell, move (into melee), and then make a melee attack (but if someone engages you in melee before the spell goes off, your casting is delayed to the miscellaneous phase and the other actions become impossible).

COMBAT SYSTEM DESIGN NOTES

OD&D doesn’t include a system for determining the order in which actions are resolved. My initial impulse was to embrace a system of simultaneous action resolution. We went through several variants of this — generally with a guideline that incapacitation favored the PCs (either striking one last valiant blow before falling unconscious or preventing monsters from dealing damage by slaying them first) — and what I discovered was that I could generally manage the system as long as the number of combatants remained relatively small.

But as group size grew — both due to the popularity of the open table and the increasing number of henchmen and hirelings — it became more difficult to juggle all of the disparate elements into a compelling narrative and game experience. This led to a fresh round of experimentation. Throughout this process I resisted the impulse to simply embrace initiative checks and call it quits (largely because I view my OD&D experiences as a chance to radically experiment with the basic game-form).

I eventually settled on this system, which is largely inspired by the Mmmmmm! System from Swords of Minaria and the Perrin Conventions. Resolution in each phase is simultaneous, but sufficiently broken up that I can manage much larger groups without losing all sense of cohesion and comprehension.

These house rules — and more! — can be found in the Blackmoor Player’s Reference.

A couple months ago I mentioned that I had created counter-intelligence guidelines for the Gather Information skill. Confanity had mentioned that he was intrigued by them, and I promised to get them posted sooner rather than later. For certain definitions of “sooner” and “later”, I suppose that this has now been accomplished.

Counter-Intelligence: A character can attempt to detect other characters gathering information about a particular subject in the area by making a Gather Information check. The DC of the counter-intelligence check is opposed by the original Gather Information check made in the attempt to gather the information.

Avoiding Suspicion: If a character is attempting to avoid suspicion, it becomes more difficult to detect them. Although the character suffers a -10 penalty on their Gather Information check for the purposes of collecting the information they seek, they gain a +10 bonus to their Gather Information check for the purposes of opposing the counter-intelligence check.

In addition, cautious characters can voluntarily increase the penalty on their original Gather Information check, granting an equal bonus for the purposes of opposing the counter-intelligence check. (For example a character could decide to be extra cautious and apply a -15 penalty to their Gather Information check. Their unmodified check result is 30, which is modified to 15 (30 – 15) for the purposes of determining what information they actually glean. But if another character attempts to detect their presence, they would have to make a DC 45 (30 + 15) counter-intelligence check to do so.)

Modifiers: Apply a -2 penalty to counter-intelligence checks for every week that has passed since the original Gather Information check.

USING THE GUIDELINES

For PCs, these guidelines aren’t only useful to find out if someone is asking questions about them. In fact, they’re generally more useful for identifying competing interests. Who else in town is trying to find out information about the Vault of the Dwarven Kings? Or investigating the Baker’s Street Gang?

Resolving these types of checks requires the GM to know two things:

(1) Who else is looking for that information?

(2) What should the DC of the check be?

The answer to the former question, of course, is situational. For the latter you could either set simple, static DCs as you would for any other Gather Information check, or you could actually resolve the opposed check.

FACTION

I generally find it useful to know what kind of information-gathering capacity factions have in my campaigns. For smaller factions (like an opposing group of adventurers or a small gang of bad guys), this is as simple as looking at the highest (or most appropriate) Gather Information skill modifier in the group.

For larger factions, I simply assign a Gather Information modifier to the group. (This number is essentially arbitrary, although I base it on the size, nature, and resources of the group in question.)

When trying to figure out how suspicious a particular group is (i.e., whether they’re performing counter-intelligence to make sure anyone is asking questions about them) or how pervasive their surveillance is (i.e., how often they’re making counter-intelligence checks), I’ve generally just relied on common sense to make a ruling whenever the question needs to be answered. But if you’re running a campaign where intelligence and counter-intelligence is likely to be fairly common (for example, a modern espionage campaign), then codifying those factors might be useful.

(For example, a Paranoid group might check 1/day; a Suspicious group every 1d6 days; a Cautious group once every 3d10 days; a Naive group might never check. In other words, if the PCs investigate a Suspicious group then there would be a counter-intelligence check made 1d6 days later.)