The Game System

“Skill rolls” may be called for during dramatic situations in the game. Walking down a well-lit hallway is not a dramatic situation, whereas running down a rubble-strewn corridor while being chased by monsters most definitely is!

When attempting a skill roll, you should agree a goal with the Keeper. If your skill roll is successful, you achieve your goal. Additionally, when you successfully roll a given skill, put a check mark in the box next to it on your investigator sheet. You can only get one check per skill at a time. At the end of the scenario, that skill could increase due to experience—see Rewards of Success, for further information.

On occasion, you may need to roll a test that is not covered by the skills on your sheet. If so, look at your investigator’s characteristics and determine which one of them is best to use and treat it like a skill.

Roleplaying Dice

Call of Cthulhu uses a set of roleplaying dice. These “polyhedral” dice include: percentage dice (D100), a four-sided die (D4), a six-sided die (D6), an eight-sided die (D8), and a twenty-sided die (D20). Dice sets can be purchased at most hobby game stores and online, and there are also online dice rollers too.

The letter “D” stands for “dice.” The number after the D is the range of numbers available: 1D8 generates random numbers 1 through 8, for instance, while 1D100 generates the numbers 1–100.

In a written adventure, the text might say a monster delivers 1D8 damage, meaning that a 8-sided die is rolled once to determine how much damage is actually caused.

Reading D100 (Percentage Dice)

Percentage dice usually consist of two 10-sided dice, which are rolled at the same time. One die (units) is numbered 1 to 0, the other (tens) being numbered 10 to 00. Both dice are rolled and should be read together (e.g. “30” on the tens die and “05” on the units die is read as 35%). A roll of “00” (tens die) combined with a “0” (units die) indicates a result of 100%. A roll of “00” on the tens die combined with any other roll on the units die indicates a roll of under 10%; for example, a roll of 00 on the tens die and 3 on the units die is read as 3%.

Dice Roll Variations

Sometimes a dice notation is preceded by a number other than “1.” This means that more than one die is rolled and that their results should be added together. For instance, 2D6 means that two 6-sided dice are rolled and totaled (or roll a D6 twice and add the scores together).

You might also see 1D6+1, for instance. This means that the number following the plus sign should be added to the result of the D6 roll. For 1D6+1, the result must be 2, 3, 4, 5, 6, or 7. If a monster claws for 1D6+1+2D4 damage, find the power of the actual attack by rolling the two requested dice, totaling the results, and adding 1 (rolling 1D6 and 2D4, then adding 1 to the total rolled).

Skill Rolls and Difficulty Levels

Your Keeper will tell you when you should attempt a skill roll and how difficult the task is.

• A regular task requires a roll of equal to or less than your skill value on 1D100 (a Regular success).
• A difficult task requires a roll result equal to or less than half your skill value (a Hard success).
• A task approaching the limits of human capability requires a roll equal to or less than one-fifth of your skill value (an Extreme success).

If you can justify it through your investigator’s actions, you can “push” a failed skill roll. Pushing a roll allows you to roll the dice a second time; however, the stakes are raised. If you fail a second time, the Keeper gets to inflict a dire consequence upon your character. Before a pushed roll is made, the Keeper has the option of foreshadowing what might happen if the pushed roll is failed; the player can then decide whether it’s worth the risk to take the second roll or not.

Example: your investigator is trying to lever open the heavy stone door of a crypt. The Keeper decides this is very difficult and asks for a STR roll, specifying that a “Hard success” is required. Your investigator’s STR is 60, so a Hard success requires a roll of 30 or below. You roll the dice but the result is 43—you have failed, as you rolled above half your investigator’s STR. You ask if you can push the roll, stating that your character is picking up and using a spade to help lever the door. The Keeper permits a second roll, but warns you that if you fail this roll, not only will the door still be closed but “something” may hear you and could be coming for your blood!

Opposed Skill Rolls

If two investigators are opposing one another, or if an investigator is in a conflict with a significant Keeper-controlled character (an NPC, i.e. one for whom statistics are listed in the scenario), the Keeper may require an “opposed roll.”

To resolve an opposed roll, both sides make a skill roll and compare their level of success. A Regular success beats a Fail, a Hard success beats a Regular success, and an Extreme success beats a Hard success. In the case of a draw, the side with the higher skill value wins. If both skills are equal, then have both sides roll 1D100, with the lower result winning.

Bonus and Penalty Dice

Sometimes, the prevailing conditions for the investigators, their environment, and/or the time available to them can hinder or benefit a skill or characteristic roll. Under certain conditions the Keeper may grant a “bonus” or a “penalty” die to a roll. One bonus die and one penalty die cancel each other out. Such bonuses and penalties operate in a similar way to raising the difficulty of a roll, and can be used instead of, or in addition to, an increased difficulty. Normally, though, bonus and penalty dice are used primarily with opposed rolls.

For each bonus die

Roll an additional “tens” percentage die alongside the usual pair of percentage dice when making a skill roll. You are now rolling three separate dice: one “units” die and two “tens” dice. To take benefit of the bonus, use the “tens” die that yields the better (lower) result.

Example: two rival investigators, Malcolm and Hugh, are vying for the affection of Lady Greene. Only one can gain her hand in marriage, so the Keeper determines that an opposed roll is needed to determine the outcome of their wooing. It is decided that each should make an opposed Charm roll. The Keeper reviews the events of the scenario so far: Malcolm has visited Lady Greene twice, each time lavishing expensive gifts upon her, while Hugh has only visited once and brought no gifts at all. The Keeper states that Malcolm has an advantage and will receive a bonus die in the opposed roll. Hugh’s player rolls first against his Charm skill of 55, getting 45—a Regular success.

Malcolm’s player rolls against his Charm skill with one bonus die, rolling one units die and two tens dice. The units die reads 4 and can be paired with either of the two tens dice to give scores of 44 or 24. Malcolm’s player takes the lower result 24—a Hard success.

Malcolm wins the opposed roll, and his proposal of marriage to Lady Greene is accepted.

For each penalty die

Roll an additional “tens” percentage die alongside the usual pair of percentage dice. You’re now rolling three separate dice: one “units” die and two “tens” dice. For a penalty, use the “tens” die that yields the worse (higher) result.

Example: in a dire turn of events, two investigators—Felix and Harrison—have been captured by the cultists of the Scarlet Smile. The cultists decide to have some “fun” at the investigators’ expense, decreeing that both must undertake the Ordeal of Pain, from which only one can survive. The loser will be sacrificed to the cultists’ foul god.

The Ordeal of Pain involves lifting a huge rock and holding it aloft. Whoever holds the rock up the longest will win. This requires an opposed STR roll from each of the investigators; however, the Keeper rules that Harrison must take a penalty die, as he recently suffered a major wound (he received an injury when he was captured by the cultists) and is still recovering.

Felix’s player rolls 51 against STR 65—a Regular success.

Harrison’s STR is 55. His player rolls 20 and 40 on two tens dice and 1 on the units die, which can be combined to read 21 or 41. The extra die was a penalty die, so Harrison must take the higher result—a Regular success

Both players have achieved a Regular success; Felix wins because he has the higher STR value. Felix is able to hold the rock above his head for longer than Harrison. The cultists jeer and lead Harrison off towards their altar...

Luck Rolls

Luck rolls may be called for by the Keeper when circumstances external to an investigator are in question, and also when determining the fickle hand of fate. If, for example, an investigator wants to know if there is an item lying nearby that they could use as weapon, or if the flashlight they have found has any juice left in it, then call for a Luck roll. Note that if a skill or characteristic is more appropriate to a situation, then it should be used rather than Luck. To succeed in a Luck roll, the investigator must roll equal to or under their current Luck value.

If the Keeper calls for a “group Luck roll,” the player whose investigator has the lowest Luck score (among those present in the scene) should make the roll on behalf of the group.

Example: finding a cab doesn’t require a dice roll, but getting one before the investigators lose sight of the car that they wish to pursue could. Credit Rating could be a factor in attracting the attention of a cabdriver on the lookout for a well-dressed fare who may tip generously. However, quickly getting a ride at two o’clock in the morning on the undesirable side of town might not be so easy. Would there even be a cab to hail? No skill is going to make a cab appear at that moment. It is a matter of chance whether a cab may be driving down that road, hence a Luck roll is required.

Quick Reference Chart For Half and Fifth Values

Find the characteristic or skill value under the Base Number column, and read across to determine the half (Hard) and fifth (Extreme) values.

Base Number	Half Value (½)	Fifth Value (1/5)	Base Number	Half Value (½)	Fifth Value (1/5)
1	0	0	51	25	10
2	1		52	26
3			53
4	2		54	27
5		1	55		11
6	3		56	28
7			57
8	4		58	29
9			59
10	5	2	60	30	12
11			61
12	6		62	31
13			63
14	7		64	32
15		3	65		13
16	8		66	33
17			67
18	9		68	34
19			69
20	10	4	70	35	14
21			71
22	11		72	36
23			73
24	12		74	37
25		5	75		15
26	13		76	38
27			77
28	14		78	39
29			79
30	15	6	80	40	16
31			871
32	11		72	36
33			83
34	17		84	42
35		7	85		17
36	18		86	43
37			87
38	18		88	44
39			89
40	20	8	90	45	18
41			91
42	21		92	46
43			93
44	22		94	47
45		9	95		19
46	23		96	48
47			97
48	24		98	49
49			99
50	25	10	100	50	20