The referee may use a character’s ability scores to determine the character’s chance of succeeding at various challenging tasks (e.g. climbing a rope, recalling a forgotten detail).

The player must roll 1d20 and try to get equal or under the appropriate ability score. A result greater than the ability score is a failure.

The referee may apply modifiers to the roll, depending on the difficulty of the task: a –4 modifier for an easy task or +4 for a difficult task. (Alternatively, the ability score being tested can be modified for the purpose of this check: up to –4 for a difficult task or up to +4 for an easy task.)

A natural 1 always succeeds and a natural 20 always fails.