An Incomplete but Helpful List of Easily Ported Rules (WIP)

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I have no idea what this little project is going to turn into... probably a searchable blog or database once I have gotten a little further into it. I wanted to list a series of optional rules I've run across in the Indie TTRPG scene that I find valuable, including where they can be found, what genres they might best be used in, and some keywords for playstyles.

This is going to be a living project where I add a few every once in awhile, and see how it evolves.

I will not include material I have seen presented as an optional rule in the core book of a current pooular TTRPG. For example, I do not include Advantage / Disadvantage because it is a rule in the core of D&D5e, and readily visible to anyone in the TTRPG community. This is meant to draw attention to options you might not have discovered. 

In each entry I have a "Find it In" section; this does not list the original appearance of the mechanic. Instead I list where I have seen interesting, innovative presentations of the mechanic. I give priority to games that are free, open culture, or at least have a downloadable quick start manual, or that cost less than $10. And I link to where the rules can be accessed most easily in my experience. 

I also have sample Keywords that cover descriptions of kind of feel or experience the mechanic supports. If a rule works well to make a campaign feel "Dark", then that is where I list it. This will let you easily use this list with the Poster Pitch tool I have presented in part one of my two-part guide to rules hacking. 

Likewise I have listed common genres of TTRPG that this specific rule will support well. 

I ask you for your feedback: Is this a project worth expanding and developing

An expanded, indexed blog version of this list is now avaliable 

Spell Rolls

Description: Make a roll similar to an skill roll to cast a spell, rather than automatically succeeding. Failed roll either cause the caster to forget the spell, deplete a power source, or have a misfire. 
Find it in: Dungeon Crawl Classics RPG, ICRPG Core 2e, the Black Hack, Dungeon World
Keywords: Weird, Fantastical, High Magic, Dark
Genres: Sword & Sorcery, Eldritch Horror, Low Fantasy

Spell Duels

Description: Usually works alongside Spell rolls, allows two Magicians to engage in a battle of wills, trying to overwhelm the other with the power of their minds until one magician breaks and the other hits with a spell. Often with weird magical crossfire. 
Find it in: Dungeon Crawl Classics RPG
Keywords: Weird, Fantastical, High Magic, Dark, Pulpy
Genres: Sword & Sorcery, High Fantasy

Roll to Recover

Description: While resting, characters make rolls to gain back health, regain lost class feature uses,  instead of automatically gaining health or abilities back; often a limited number of rolls per day. Reduces the temptation for resting after encounters and reduces the power of resting. 
Find it in: Low Fantasy Gaming 
Keywords: Weird, Fantastical, High Magic, Dark

Genres: Sword & Sorcery, High Fantasy, Western

Let the Shield be Shattered

Description: Sacrifice a shield to reduce the damage of an attack. 
Find it in: ICRPG Core 2e, the Black Hack
Keywords: Fantastical, Tactical, Heroic, Cinematic, Swashbuckling 
Genres: Sword & Sorcery, High Fantasy, Low Fantasy, Science Fiction

Let the Mail be Rent

Description: Sacrifice Armor effectiveness to reduce damage. 
Find it in: Right Here
Keywords: Fantastical, Tactical, Heroic, Cinematic, Swashbuckling 
Genres: Sword & Sorcery, High Fantasy, Low Fantasy, Science Fiction, Post-apocalyptic, Pulp

Encumbrance Slots

Description: Instead of measuring gear by weight, give PCs a limited number of slots, either fixed or stat-based, in which items can be carried. Small items might fit in a single slot. Armor and very large items in multiples. 
Find it in: Lamentations of the Flame Princess, Knave, Maze Rats, Mausritter 
Keywords: Rules-light, Cinematic,
Genres: Any

Mighty Deeds of Arms

Description: Combat-oriented characters may declare special effects of a combat attack, like disarming, knock back, tripping, blinding, etc., and get variable success based on a roll of a die. 
Find it in: Dungeon Crawl Classics RPG
Keywords: Weird, Fantastical, Dark, Tactical, Swashbuckling 
Genres: Sword & Sorcery, High Fantasy, Low Fantasy, Post-apocalyptic, Science Fiction, Pulp, Superhero

Combat Exploits

Description: During Combat characters may declare special effects of a combat attack, like disarming, knock back, tripping, blinding, etc., and on a successful attack, a die roll may resolve this effect. More severe or permanent effects may require special Luck checks or limited resources. Missed exploits prevent further exploits against a target until players gain  new tactical advantage. 
Find it in: Low Fantasy Gaming
Keywords: Tactical, Swashbuckling, Heroic, Pulpy
Genres: Sword & Sorcery, High Fantasy, Low Fantasy, Post-apocalyptic, Science Fiction, Pulp, Superhero, Western

Intercepting

Description: A character may sacrifice their turn to run their movement speed and block another moving character from reaching their destination. 
Find it in: Low Fantasy Gaming
Keywords: Tactical, Swashbuckling, Heroic
Genres: Any

Rescues

Description: A character may sacrifice their turn and a resource like luck to leap to another NPCs aid, catching them at a cliff's edge, pushing them out of the way of a car, taking a bullet for them. Etc. PC preforming the rescue may be subject to taking damage themselves. 
Find it in: Low Fantasy Gaming
Keywords: Tactical, Swashbuckling, Heroic, Pulpy
Genres: Sword & Sorcery, High Fantasy, Low Fantasy, Post-apocalyptic, Science Fiction, Pulp, Superhero, Military

Luck Scores

Description: Characters have a depleting pool of Luck that may or may not Regenerate over time or as a RP reward. When no other roll seems appropriate to determine outcome, Luck can be rolled to see if a PC catches a break. It may be spent for bonuses. May replace saving throws. 
Find it in: Low Fantasy Gaming, Dungeon Crawl Classics RPG, Troika! 
Keywords: Pulpy
Genres: Any

Daily Re-Roll

Description: Players have a single per session ability to force the re-roll of a single die. 
Find it in: Common House Rule
Keywords: - 
Genres: Any

Re-Roll Pools

Description: Player's have a refreshing pool of times they may re-roll checks, applicable only to specific abilities of the character (like proficiencies), or Luck Checks. Replaces skill system and saving throw specialization. 
Find it in: Low Fantasy Gaming
Keywords: Rules-light
Genres: any

Lingering Injuries and Dismemberments

Description: Once knocked out of commission in combat, a character has a chance of suffering lingering or permanent injuries that create penalties to the character or stat reductions. 
Find it in: Dungeon Crawl Classics RPG, the Black Hack, GLOG
Keywords: Dark, Gritty, Pulpy
Genres: Sword & Sorcery, Pulp, Military, Post-apocalyptic, Science Fiction

Room Target Numbers

Description: Set a single d20 target number for all tasks in a room or for an encounter, allowing for modifiers based on the difficulty of the task being rolled for ease of tracking and play. Often made visible to players. 
Find it in: ICRPG Core 2e, 
Keywords: Rules-Light, Fast-Paced
Genres: Any

Progress Clocks

Description: Any task that requires more than a single roll, or a hazard that players may accidentally manifest through their action, are expressed a multi-part counter with 4-8 segments depending on complexity. A character fills 1-3 based on a degree of success with tasks until the click is filled, at which point the task is complete or the hazard comes to pass. 
Find it in: Blades in the Dark 
Keywords: Fast-Paced
Genres: Any

Effort Pools

Description: Setting a hit point total for a challenge that requires time and multiple rolls can be expressed as a hit point total. Characters' actions can thus be expressed as damage toward the total, making a single consistent mechanic for all tasks. 
Find it in: ICRPG Core 2e, 
Keywords: Rules-Light, Fast-Paced
Genres: Any

Depletion Dice

Description: Instead of tracking individual items like money, rations, and ammunition, a die can be expressed as a die. Each time the resource is taxed, the die is rolled to test whether that resource has been reduced in quantity, which is represented bt replacing the die with a smaller one on a dice chain. After a d4 fails a roll to avoid depletion, the resource is lost. Offers a visual way to track resources. 

Find it in: the Black Hack, Tiny Dungeon 2e 
Keywords: Rules-Light, Fast-paced, Cinematic, Pulpy
Genres: Any

Depletion Dice (Light) 

Description: Using a modification of the depletion dice, combustible light sources can be given a variable duration. 
Find it in: The Delve 2e
Keywords: Rules-Light, Fast-paced, Dark, Tense
Genres: Sword & Sorcery, Western, Low Fantasy, Post-apocalyptic, Horror 

Madness

Description: A staple of Lovecraftian Horror, madness rules can be fairly easily ported to other systems.  Some rely on a limited sanity resource, are connected to injury tables, or magical misfire effects. All add role-playing constraints and mechanical consequences. 
Find it in: Low Fantasy Gaming, Call of Cthulhu, Tiny Cthulhu 
Keywords: Dark, Weird, Horror
Genres: Sword & Sorcery, Eldritch Horror, Dark Fantasy, Horror

Randomized Levelling

Description: When leveling, a character rolls randomly for mechanical advancement, to make individual characters more unique. 
Find it in: Lion and Dragon, Star Adventurer 
Keywords: Old-School 
Genres: any

Flashbacks

Description: This system allows PCs to expend resources and risk harm to have an action occur in the past that gives the PC an advantage or potential solution in the present. Allows the PCs to dive directly into action and get the benefits of an extended planning session. 
Find it in: Blades in the Dark 
Keywords: Fast-Paced
Genres: Crime, Military, Cyberpunk, Western

Engagement Rolls

Description: Stands in for a planning session, this roll allows a battle, heist, or similar planning-intensive adventure. The roll establishes the danger level and task difficulty as the adventure begins in media res. 
Find it in: Blades in the Dark 
Keywords: Fast-Paced
Genres: Crime, Military, Cyberpunk

Armor Points

Description: Used in games that use hot points, wound levels, or damage tracks, Armor adds additional damage to the total the character can take that cannot heal unless the armor is repaired. 
Find it in: Blades in the Dark, Tiny Dungeon 2e, Pacts and Blades 
Keywords: Fast-paced, Tactical, Cinematic
Genres: Crime, Military, Sword and Sorcery, Low Fantasy, Science Fiction

Armor as Damage Reduction

Description: Rather than having armor make a PC harder to damage or letting them take more, armor reduces the amount of damage taken on each attack, or allows characters t soak more damage if resistance rolls are used. 
Find it in:  the Black Hack, Shadowrun, World of Darkness, Into the Odd
Keywords: Heroic, Epic, Pulpy
Genres: High Fantasy, Epic Fantasy, Science Fiction, Superhero, Pulp

Depleting Armor

Description: Armor is subject to depletion dice or a similar mechanism to become weaker over time as it is used. 
Find it in:  the Black Hack, Shadowrun 
Keywords: Gritty, Dangerous, Dark, Survival
Genres: Sword and Sorcery, Cyberpunk, Western, Post-apocalyptic, Horror

Carousing

Description: Characters may spend a randomized amount of treasure to go on a bender, earning XP or other rewards. Causes a roll on a random table to describe events and the Fallout of the character's wild debauch. 
Find it in:  Ultraviolet Grasslands and the Black City, DCC HUBRIS, GLOG
Keywords: Exploration, Light-Hearted
Genres: Sword and Sorcery, Western, Post-apocalyptic

Simultaneous Initiative

Description: Players declare their actions without establishing initiative; the GM resolves all events in a phase order as if they happened nearly simultaneously. Creates a situation where combat is realistically confusing. 
Find it in:  Dungeoncraft, Dungeon World
Keywords: Dark, Gritty, Dangerous, Fast-Paced
Genres: Sword and Sorcery, Post-apocalyptic, Low Fantasy 

Timed Initiative

Description: Players have a limited time to declare their action. If they do not have one to declare, they default to a defensive action.  Often used in conjunction with Simultaneous initiative. 
Find it in:  Dungeoncraft, Dungeon World
Keywords: Dark, Gritty, Dangerous, Fast-Paced
Genres: Sword and Sorcery, Post-apocalyptic, Low Fantasy 

Zones - Objective

Description: Distance is abstracted into either three zones: near, far, and close or into two zones: here and there. The center of an encounter with the most action is counts as close, being at range to use short-range weapons and reach weapons places you at near, while ranged weapons and Magic attacks only places you at far. Or, being close enough to use a melee weapon is here, and being far enough away to use a ranged weapon is there. Movement, magic effects, Etc are abstracted to to work with this system. In some games this is interchangeable with subjective zones. 

Find it in: the Black Hack, Tiny Dungeon 2e, ICRPG Core 2e, 5e Hardcore Mode
Keywords: Rules-Light, Fast-paced
Genres: Any

Zones - Subjective

Description: Movement, reach, attack ranges, and spell effects are measured in zones: close, near, and far. Each is a relative distance from the character currently acting. So, close is close enough for the character in question to touch or engage in melee after just a few steps. Near is within range for a short-range spell a reach weapon or a sling. Far is something distant enough to require a bow or spell to attack and is too far to walk to and act in the same round. In some games this is interchangeable with objective zones. 

Find it in: the Black Hack, ICRPG Core 2e, Tiny Cthulhu
Keywords: Rules-Light, Fast-paced
Genres: Any

Player-Facing Defense

Description: Game masters do not roll for attack, instead PCs have a defense ability they roll when attacked to beat a set attack value from a monster. 
Find it in: Knave, Maze Rats, Four Against Darkness, the Black Hack
Keywords: Rules-light, Heroic, Tactical
Genres: Any

Wounds 

Description: Hit points are abstracted either into the number of Wounds that the target can take (in OSR games this is equal to HD). Any hit doing 4 or more damage deals a wound.
Find it in: Dungeoncraft
Keywords: Rules-light, Heroic, Fast-Paced
Genres: Any

Panic!

Description: Characters trapped without light underground experience extreme terror that can cause confusing, trauma, or even death from the fear. 
Find it in: the Black Hack
Keywords: Dark, Horrific, Dangerous, Gritty, Survival
Genres: Sword & Sorcery, Eldritch Horror, Survival, Horror

Abstract Coin

Description: Treasure is abstracted from numbers of coin, gem, jewels, and artifacts into a Wealth statistic that a character checks against to buy items, often depleting on a failed roll. Often used in conjunction with depletion dice. 
Find it in: the Black Hack, Tombpunk
Keywords: Rules-light, Epic, Pulpy
Genres: Sword & Sorcery, Epic Fantasy, Pulp, Superhero

Failing Forward

Description: Task resolution rolls that do not indicate success do not mean simply failure that halts forward momentum; instead it means the PCs suffer loss of equipment, injury, or discover another way to progress that creates even more obstacles. A failed roll leads to a narrative complication, not a halt to the action. 
Find it in: the Black Hack, PARANOIA 2017, 
Genres: High Fantasy, Epic Fantasy, Pulp, Superhero
Keywords: Heroic, Light-Hearted, Pulpy

Pact Magic

Description: Spells are replaced by relationships with spirits that have broad spheres of influence. The spirit may be called on to create any plausible effect that fits with its domain, allowing PCs to come up with inventive magical effects within a narrow scope. 
Find it in: Pacts and Blades, World of Dungeons 
Keywords: Rules-light, Dark, Pulpy, Horrific
Genres: Sword & Sorcery, Low Fantasy, Pulp, Horror

Evolving Magic Items

Description: Magic items are exceedingly rare. They begin with a single ability, but gain more abilities as their wielder levels up, allowing magic items to grow with PCs, rather than having PCs find many of them. 
Find it in: Low Fantasy Gaming
Keywords: Weird, Pulpy, Dark, Heroic
Genres: Sword & Sorcery, Low Fantasy