Difficulty Modifiers

This rule is inspired by RuneQuest, 3rd Edition, © 1984 by Chaosium, Inc., and published by Avalon Hill.

General Rule

A character's skill level represents the chance of the character succeeding in a skill under "normal" stress levels. The Keeper can alter this percentage by adding or subtracting percentiles from a character's skill.

For instance, if a character is climbing an incline, the character's Climb skill may be modified by -20% if the incline is particularly steep or the footing is crumbly. A Mechanical Repair (or Locksmith, if using the optional Pagan Publishing rules) skill may be modified by -25% if the lock is particularly difficult or if the locksmith doesn't have his tools.

Likewise, skills can be modified by adding skill percentages. If a character has pitons to help climbing, a +20% modifier may be appropriate. If a lock is cheap and fairly easy to pick, a Keeper may assign a +30% chance to open it.

A player may also decide that a skill can be modified by doubling the skill percentage, or by reducing it by half or by a quarter. This is how weapon skills are altered due to range.

A skill check is allowed for all skills that succeed, even those with positive modifiers.

Specific Skill Modifiers

The following modifiers are suggested for use with specific skills.

Hide Skill

The Hide skill is modified as follows:

Sneak Skill

The Sneak skill is modified as follows:

Spot Hidden Skill

The Spot Hidden skill is modified as follows:

Track Skill

The Track skill is modified as follows:

Weapon Skills

For weapon skill modifications, see the Shooting Modifiers house rules page.


Design Notes

The rule for adding or subtracting percentages is taken from 3rd Edition RuneQuest, which uses the same system as Call of Cthulhu (the Chaosium Basic Role Play system). While never formally mentioned in the Call of Cthulhu rules, they are there in spirit. In Call of Cthulhu 5.5 Edition the chase rules have situational modifiers that add or subtract percentages from a character's drive skill. Modifiers are also found in some Call of Cthulhu scenario and campaign packs.

The Keeper is given a lot of latitude in deciding the penalty or bonus to a specific skill. This is how it's done in RuneQuest as well as other roleplaying games that allow skill modifiers due to difficulty. In general, only exceptional circumstances should have a skill modifier.