Some ideas for using the Dungeons & Dragons B/X rules from 1981, which also fit Old-School Essentials, Basic Fantasy Role-Playing Game, and similar OSR retroclones.
ABILITY TASK ROLLS (skills, aptitudes)
Instead of the “roll d20 under your Ability Score” rule, I prefer to keep the “roll high is good, low is bad” mechanic. With that in mind, roll 1d20 and add the full Ability Score (not just the modifier). For random NPCs, use 1d20+Hit Dice for primary scores, 1d20+half Hit Dice for secondary scores. Any result equal to or greater than the target number set by difficulty mean the task succeeds.
* Very Easy … total 10 or better
* Easy … total 15 or better
* Medium … total 20 or better
* Hard … total 25 or better
* Very Hard … total 30 or better
* Extreme … total 35 or better
Critical Results
* A “natural 1” always adds a complication, even if the roll total succeeds.
* A “natural 20” always adds an unexpected benefit, even if the roll total fails.
Quick Modifiers (straight from D&D5E rules)
* Advantage: Roll two d20s and only use the higher rolled number.
* Disadvantage: Roll two d20s and only use the lower rolled number.
* Multiple causes of Advantage or Disadvantage only add one additional die to the task roll.
* Causes of Advantage and Disadvantage on the same task roll cancel out.
HIT POINTS, DYING, AND RECOVERY
* In addition to boosting hit points, Constitution also extends how long a person lingers at the edge of death when at 0 or less hit points.
* Death: At 0 hit points, creatures become unconscious and dying. Machines are inoperable. After a number of round equal to a dying creature’s Constitution score, the creature permanently dies.
* Aid: A dying creature may be given aid once per round before death to recover a number of hit points equal to the dying creature’s Constitution score + the aiding character’s Level. Once current hit points reach 1 h.p., aid no longer restores lost hit points. Magical healing that restores to 1 h.p. or more also saves a dying creature.
* Natural Healing: Per hour of rest, a creature recovers 1 h.p. per Level. Double the recovery rate under medical care (hospital, med bay).
SAVING THROWS (other hazards that fit)
* Poison/Death Ray (also toxins, diseases, radiation)
* Magic Wand (also energy shocks, electrical power currents)
* Turn to Stone/Paralysis (petrification, Tasers)
* Dragon Breath (also catastrophes, explosions, collapsing buildings, vehicle crashes)
* Spells/Magic Staff (any anomalies, exposure to eldritch dimensions)
ALTERNATE RANGE MODIFIERS
* +2 … Touching: Held, grappled, connected
* +0 … Melee Range: Up to 6 feet (2 meters) (assumes attack can move)
* -1 … Throwing Range: 50 feet (15 m) (hand axes, spears, shotguns)
* -2 … Short Shooting: 330 feet (100 m) (bows, javelins, pistols)
* -4 … Long Shooting: 2,000 feet (600 m) (rifles, beam weapons)
* -8 … Distant Range: 15 miles (25 km) (artillery, cannons)
MOVEMENT
Not a house rule, more just clarification using the “basic encumbrance” optional rule…
* Base Movement Rate: Exploration rate (cautious, searching for secret doors along the way) in a turn. Used for exploration decisions.
* Encounter Movement Rate: Move and attempt one action per round. (Triple to base rate for just running without other actions, like the 5E “Dash” action). Used for combat decisions.
* Overland Movement Rate: 1/5 base rate equals miles per day (or roughly 1/3 rate equals km per day). Used for travel decisions.
* Special Moves: Reduce by half if crawling, climbing, swimming, or moving through hindering terrain (ice, swamps, rubble, crowded rooms).
Default (human) movement
* Base Rate: 120′ per 10-minute turn (36 meters per turn)
* Encounter Rate: 40′ per 10-second round (12 meters per round)
* Overland Travel: 24 miles per day (38 km per day)
Movement modifiers
* Light Encumbrance: -30′ (-10′) (-9m (-3m)) (wearing light armor or carrying load)
* Medium Encumbrance: -60′ (-20′) (-18m (-6m)) (wearing medium or heavy armor, or light with load)
* Heavy Encumbrance: -90′ (-30′) (-27m (-9m)) (wearing medium or heavy armor and carrying load)
* Small humanoid: -60′ (-20′) (-9m (-3m)) (dwarf, gnome, goblin)
Note 1: “Load” means carrying more than 40 lbs. (18 kg), or see the expanded Strength chart below to determine “load” thresholds.
Note 2: Halflings, although small, move at 90′(30′).
Move Conversions: B/X = AD&D1e = 3.5/5E
(Follows the spirit of the rules more than the math.)
* 180′(60′) = 18″ = Speed 40 ft.
* 150′(50′) = 15″ = Speed 35 ft.
* 120′(40′) = 12″ = Speed 30 ft.
* 90′(30′) = 9″ = Speed 25 ft.
* 60′(20′) = 6″ = Speed 20 ft.
* 30′(10′) = 3″ = Speed 15 ft.
ARMOR CLASSES [Ascending Armor Class]
* AC 9 [AAC 10] … No armor
* AC 8 [AAC 11] … Shield only
* AC 7 [AAC 12] … Light armor (leather)
* AC 6 [AAC 13] … Light armor + shield
* AC 5 [AAC 14] … Medium armor (chainmail)
* AC 4 [AAC 15] … Medium armor + shield
* AC 3 [AAC 16] … Heavy armor (plate)
* AC 2 [AAC 17] … Heavy armor + shield
* AC 1 [AAC 18] … Extreme armor
* AC 0 [AAC 19] … Extreme armor + shield
COMBAT “TO-HIT” MODIFIERS
* +Strength modifier … melee weapons
* +Dexterity modifier … ranged weapons
* +1 … ranged weapons, short range
* -1 … ranged weapons, long range
* -2 … non-proficient weapon (martial class; 1d8 hit die)
* -3 … non-proficient weapon (semi-martial class; 1d6 hit die)
* -5 … non-proficient weapon (non-martial class; 1d4 hit die)
* -2/-4 … dual wielding
SIMPLIFIED WEAPON DAMAGE (all d6 based)
* 1d6 x0.5 … Light weapon (dagger, thrown stone)
* 1d6 … Medium weapon (axe, sword, mace, staff, pistol)
* 1d6 x2 … Heavy weapon (greatsword, pole arm, rifle)
ALTERNATE INITIATIVE
* NPCs and creatures have a default initiative score equal to 10 + Hit Dice. If an encounter has mixed opposition, use the highest Hit Dice individual among the group.
* Characters roll d20, modified by Dexterity (3 or less, -2; 4 to 8, -1; 9 to 12 no adjustment; 13 to 17, +1; 18 or more, +2).
* Characters rolling equal to or higher than the opposition may act before the NPCs/creatures in any order.
* Characters rolling below the opposition’s initiative act after the NPCs/creatures in any order.
FIGHTERS IN COMBAT
* As per B/X, fighters still only get one attack roll per round.
* Fighters add their Level to damage for the round.
* Total damage may be applied to multiple targets hit by an attack roll (anything within melee reach or weapon range with an Armor Class hit at or below the d20 roll). For any target reduced to 0 hit points, remaining damage may be applied to any other available targets.
* Example: A 5th-level fighter with a longsowrd attacks a band of a dozen goblins (each with 3 h.p.). The fighter roll at 17 “to hit” and roll the sword’s 1d8 for 6 damage, adding +2 for Strength 16 and +5 for Level 5, for a total of 13 points of damage. The fighter slays four goblins and damages a fifth goblin for 1 h.p. (13 damage/3 h.p.).
For other martial classes…
* Paladins: +double Level damage on hits against the undead and lower-plane fields.
* Rangers: +double Level damage against a favored enemy (orcs, hobgoblins, giants) or monster (dragons).
SPECIAL COMBAT RULES (ALL CLASSES)
* Knockout: Any living target that takes damage from a single attack greater than that creature’s Constitution score must make a Death saving throw or fall unconscious for 1 to 20 rounds (d20, no modifier). Another being may give aid as a round’s action to immediately awaken one downed individual.
* Pulling Punches: An attacker may choose to do less damage than normal, but only before making the “to hit” roll against the target.
* Full Autofire: If 10 or more rounds are fired from a gun, add +3 to both the attack task roll and +6 to the damage.
COMBAT “TO-HIT” MODIFIERS (rules as written, not house rules)
* +Strength modifier … attacking unarmed, with a melee weapon, or with a thrown weapon
* +Dexterity modifier … attacking with a ranged weapon
* +1 … ranged weapons, short range
* -1 … ranged weapons, long range
* -2 … non-proficient weapon (martial class; 1d8 hit die)
* -3 … non-proficient weapon (semi-martial class; 1d6 hit die)
* -5 … non-proficient weapon (non-martial class; 1d4 hit die)
CUSTOM SPELL EFFECTS
Players may tweak descriptions to fit their characters, such as an “ice mage” knowing how to cast a “Frostball” spell (works the same as Fireball but does cold damage instead of fire). The mechanics of the spell generally remain the same, but the flavor changes.
SPELL DRAIN (simulating the health damage from magic use)
* A caster may choose to expend hit points to gain extra spell slots.
* The caster cannot gain spell slots beyond the normal maximum spell level allowed.
* The caster can expend more than current hit points, but immediately dies if at 0 or less h.p. (Thus, a caster at the verge of death could go out in a blaze of glory.)
* 1 h.p. grants one 1st-level spell casting
* 8 h.p. grants one 2nd-level spell casting
* 27 h.p. grants one 3rd-level spell casting
* 64 h.p. grants one 4th-level spell casting
* 125 h.p. grants one 5th-level spell casting
* 216 h.p. grants one 6th-level spell casting
ENCUMBRANCE LIMITS
The weight that can be carried for an extended period of time is based on a character’s Strength Ability Score. Lifting limits assumes no more than one round of effort.
* 1 Strength: Carry 2.5 lbs. (1 kg), lift 10 lbs. (5 kg)
* 2 to 3 Strength: Carry 6 lbs. (3 kg), lift 25 lbs. (11 kg)
* 4 to 5 Strength: Carry 12 lbs. (5.5 kg), lift 50 lbs. (22 kg)
* 6 to 8 Strength: Carry 25 lbs. (11 kg), lift 100 lbs. (45 kg)
* 9 to 12 Strength: Carry 40 lbs (18 kg), lift 150 lbs. (70 kg)
* 13 to 15 Strength: Carry 55 lbs. (25 kg), lift 225 lbs. (100 kg)
* 16 to 17 Strength: Carry 85 lbs. (40 kg), lift 340 lbs. (150 kg)
* 18 to 19 Strength: Carry 125 lbs. (55 kg), lift 500 lbs. (230 kg)
* 20 to 21 Strength: Carry 190 lbs. (85 kg), lift 760 lbs. (340 kg)
* 22 to 23 Strength: Carry 285 lbs. (130 kg), lift 1,140 lbs. (520 kg)
* 24 to 25 Strength: Carry 425 lbs. (190 kg), lift 1,700 lbs. (780 kg)
* 26 to 27 Strength: Carry 500 lbs. (225 kg), lift 1 ton
* 28 to 29 Strength: Carry 1,000 lbs. (450 kg), lift 2 tons
* 30 to 31 Strength: Carry 1,500 lbs. (680 kg), lift 3 tons
* 32 to 33 Strength: Carry 1 ton, lift 4 tons
* 34 to 35 Strength: Carry 1.5 tons, lift 6 tons
* 36 to 37 Strength: Carry 2.25 tons, lift 9 tons
* 38 to 39 Strength: Carry 3.25 tons, lift 13 tons
* 40 to 41 Strength: Carry 5 tons, lift 20 tons
* 42 to 43 Strength: Carry 7.5 tons, lift 30 tons
* 44 to 45 Strength: Carry 11 tons, lift 45 tons
* 46 to 47 Strength: Carry 16 tons, lift 65 tons
* 48 to 49 Strength: Carry 25 tons, lift 100 tons
* 50 to 51 Strength: Carry 37 tons, lift 150 tons
* 52 to 53 Strength: Carry 55 tons, lift 222 tons
* 54 to 55 Strength: Carry 85 tons, lift 340 tons
* 56 to 57 Strength: Carry 125 tons, lift 500 tons
* 58 to 59 Strength: Carry 190 tons, lift 760 tons
* 60 to 61 Strength: Carry 300 tons, lift 1,200 tons
* 62 to 63 Strength: Carry 425 tons, lift 1,700 tons
* 64 to 65 Strength: Carry 625 tons, lift 2,500 tons
* 66 to 67 Strength: Carry 950 tons, lift 3,800 tons
* 68 to 69 Strength: Carry 1,400 tons, lift 5,700 tons
* 70 to 71 Strength: Carry 2,100 tons, lift 8,650 tons
* 72 to 73 Strength: Carry 3,200 tons, lift 13,000 tons
* 74 to 75 Strength: Carry 4,700 tons, lift 19,000 tons
* 76 to 77 Strength: Carry 7,500 tons, lift 30,000 tons
* 78 to 79 Strength: Carry 11,000 tons, lift 44,000 tons
* 80 to 81 Strength: Carry 16,000 tons, lift 65,000 tons
* 82 to 83 Strength: Carry 25,000 tons, lift 100,000 tons
* 84 to 85 Strength: Carry 37,500 tons, lift 150,000 tons
* 86 to 87 Strength: Carry 56,000 tons, lift 225,000 tons
* 88 to 89 Strength: Carry 85,000 tons, lift 340,000 tons
* 90 to 91 Strength: Carry 125,000 tons, lift 500,000 tons
* 92 to 93 Strength: Carry 190,000 tons, lift 760,000 tons
* 94 to 95 Strength: Carry 275,000 tons, lift 1.1 million tons
* 96 to 97 Strength: Carry 425,000 tons, lift 1.7 million tons
* 98 to 99 Strength: Carry 625,000 tons, lift 2.5 million tons
* 100 to 101 Strength: Carry 950,000 tons, lift 3.8 million tons
TIME TO DO TASKS
One-Round Tasks: Pick a simple lock, find and disable a trap, stow a weapon, search a chest, or search for secret doors on a 5-foot section of wall.
One-Minute Tasks: Pick a complex lock, search a small room or a corpse, calm a frightened animal, give a rousing speech to allies, break down a door, hide a small item, loot a chest, or pack up supplies.
One-Hour Tasks: Explore one wing of a ruin, forage for food or water, set up camp and cook a meal, interrogate a captured foe, translate or decipher a manuscript or book chapter written in a foreign language, carouse in one tavern for news and rumors, repair slightly damaged armor and weapons.
One-Day Tasks: Research a topic at a library or archive, craft a basic item (worth 2 g.p. or less), build a basic structure (large tent, barricade, raft), write a detailed report or coded message, carouse across an entire town for news and rumors, set traps to fortify a location, explore or search an area 5 miles by 5 miles.
One-Month Tasks: Build a specific small structure (forge, library, safehouse), conduct an archaeological dig, train a local militia, raise funds through a trade (profession, crime, performance), write a book.
MODERN AND SCI-FI GUNS
* Pistol: 15 shots, 1d6 damage, short shooting range (up to 330 feet or 100 m).
* Shotgun: 6 shots, 1d6 x 2 damage, throwing shooting range (up to 50 feet or 15 m).
* Rifle: 10 shots, 1d6 x 2 damage, long shooting range (up to 2,000 feet or 600 m).
* Assault Rifle: 30 shots, 1d6 x 2 damage, long shooting range (up to 2,000 feet or 600 m); if 10 or more rounds are fired from a gun, add +3 to both the attack task roll and +6 to the damage.
* Laser Pistol: 100 shots, 1d6 damage, long shooting range (up to 2,000 feet or 600 m).
* Laser Rifle: 100 shots, 1d6 x 2 damage, distant range (up to 15 miles or 25 km).
Distance to horizon and altitude above ground limit range. Here’s a rough rule of thumb on seeing to the distance based on the curviture of the Earth from sea level…
* 0 ft. (ground level) … 0 miles (0 km)
* 6 ft. (human height) …. 3 miles (5 km)
* 10 ft. (deck of a ship at sea) … 4 miles (6 km)
* 30 ft. (castle wall) … 7 miles (11 km)
* 100 ft. (atop a lighthouse) … 12 miles (20 km)
* 1,000 ft. (atop a skyscraper-like tower) … 40 miles (50 km)
d20 PERCENTILE
(minimum roll needed on d20)
* 20 … 1% to 4%
* 19 … 5% to 9%
* 18 … 10% to 14%
* 17 … 15% to 19%
* 16 … 20% to 24%
* 15 … 25% to 29%
* 14 … 30% to 34%
* 13 … 35% to 39%
* 12 … 40% to 44%
* 11 … 45% to 49%
* 10 … 50% to 54%
* 9 … 55% to 59%
* 8 … 60% to 64%
* 7 … 65% to 69%
* 6 … 70% to 74%
* 5 … 75% to 79%
* 4 … 80% to 84%
* 3 … 85% to 89%
* 2 … 90% to 94%
* 1 … 95% to 99%
NUMBER IN 6
(minimum roll needed on d20)
* 17 … 1 in 6 chance
* 14 … 2 in 6 chance
* 10 … 3 in 6 chance
* 7 … 4 in 6 chance
* 4 … 5 in 6 chance
* auto … 6 in 6 chance