Ability to Act

Using ability scores to arbitrate character actions—fast and smart

Through they form the crux of D&D’s class system, ability scores are largely downplayed in the game. Outside of representing one (or two) prime requisites for characters, and (depending on which version of the game you’re playing) modifying certain attributes (like “to-hit” rolls, damage, and AC), ability scores don’t really represent much. The optional General Skills rules do bring them to the fore, though the mechanic is somewhat backwards, as it rewards low dice rolls instead of high results.

To address these issues—bringing ability scores back into focus and doing so intuitively—this article proposes a consistent system of attribute checks to handle just about any action a character might attempt. [This mechanic is a highly-distilled version of that put forth in the Dungeons & Dragons, Third Edition game, and used in the Castles & Crusades RPG, published by Troll Lord Games. I don’t profess to reinventing the wheel, though I do offer the guidelines below as an xD&D-friendly adaptation. -EDS]

Attribute Check Basics

Attribute checks are made with a 20-sided die. Each attribute check is based on one of the six character ability scores (Strength, Intelligence, Wisdom, Dexterity, Constitution, or Charisma; RC/9). Regardless of action attempted or attribute used, the target number is always 16 (i.e., an attribute check succeeds if the d20 result equals or exceeds 16). For a little extra tension, the DM may rule that a natural “20” always succeeds, while a natural “1” always fails, regardless of modifiers.

Target Numbers and Modifiers

The target number (TN) of 16 represents a 25% chance of success. However, this baseline doesn’t account for the action’s difficulty or a character’s ability.

Difficulty Modifiers
Difficulty modifiers indicate how hard an action is to perform. As such, they are always added to the d20 target number. As a rule of thumb, difficulty is a loose assignment of “level,” to the action. For example, actions opposed by a monster or character are adjusted by the monster’s HD or character’s experience level. As a guideline, apply a modifier of +1 per level up to Name level, then +1 for every three levels thereafter, as shown below:

Level or HD Difficulty Modifier   Level or HD Difficulty Modifier
1 +1   10-12 +10
2 +2   13-15 +11
3 +3   16-18 +12
4 +4   19-21 +13
5 +5   22-24 +14
6 +6   25-27 +15
7 +7   28-30 +16
8 +8   31-33 +17
9 +9   34-36 +18

Ability Modifiers
Ability modifiers represent a PC’s capability to perform an action. Such modifiers are always added to the d20 roll used to make the attribute check. The most common ability modifier is the standard ability score adjustment (RC/9) of the attribute used. If the action is made with the character’s primary attribute, the modifier improves:

Ability Score Modifier Primary Attribute
3 -3 +0
4–5 -2 +1
6–8 -1 +2
9–12 0 +3
13–15 +1 +4
16–17 +2 +5
18 +3 +6

Character level also applies as an ability modifier. Use the same guidelines as shown above (i.e., +1 per level up to Name level, then +1 for every three levels thereafter).

Using Attribute Checks

Attribute checks are best used to resolve actions not handled by another, more specific game mechanic. Examples include jumping a chasm, solving a riddle, remembering a detail, influencing an NPC via conversation, appraising something valuable, etc. When making an attribute check, subtract the ability modifier from the final target number. The difference is the d20 result required to succeed.

Erol is a 2nd-level magic-user who wants to identify the runes on a tomb entrance. The DM decides this is attribute check is based on INT, which is 15 and Erol’s primary attribute. The DM assigns a difficulty modifier of 5 (reasoning that the runes were inscribed by a 5th-level cleric long ago), so the target number is 21 [base 16 +5 = 21]. Erol’s ability modifier is +6 [+2 for being 2nd-level and +4 for INT 15 as primary). If Erol’s d20 roll is 15 or higher, his attempt to decipher the runes succeeds.

If the DM desires more consistency within his game, the attribute check system can be adapted to replace existing mechanics:

General Skills
Skill checks in this system are easy to arbitrate. Simply make an attribute check against the ability score assigned to the General Skill. Each slot spent on the skill grants an ability modifier of +1.

Consider 2nd-level magic-user Erol from above, who again wants to identify the runes on a tomb entrance. The DM allows Erol to apply his Language General Skill. Again, the check is based on INT, which is 15 and Erol’s primary attribute, though Erol also possesses Language (runic) +2. Assuming the same difficulty, the attribute check’s TN is 21, though Erol’s ability modifier is now +8 [+2 for 2nd-level, +4 for INT 15 as primary and +2 for his Language General Skill). Now, Erol needs to roll only 13 or higher to succeed.

Saving Throws
This requires tying saves to ability scores (q.v., Making the Save) and making an attribute check instead of a traditional saving throw. The level or HD of whatever forces the saving throw is always applied as a difficulty modifier (as above).

Using the same example from Making the Save, Mertrand is a 3rd-level fighter who accidentally trips a rock fall in a cavern. The DM classifies this as a Force save, and rules that Mertrand can avoid the tumbling boulders with his STR (his primary attribute). Mertrand’s STR is 13 and his save modifier is +7 (+3 for being 3rd-level +4 for STR 13 as primary). Mertrand therefore needs to roll 9 or more to make the save.

Thief Skills
The attribute check system can arbitrate basic thieving abilities by assigning each to an ability score, as shown below:

Thief Ability Attribute   Thief Ability Attribute
Open Locks DEX   Move Silently DEX
Find Traps INT   Hide in Shadows DEX
Remove Traps DEX   Pick Pockets DEX
Climb Walls STR   Hear Noise INT

This opens the possibility of allowing non-thieves to practice such skills. This approach isn’t necessarily unbalancing, though to reflect the superiour training thieves receive, only thief characters may apply their experience level bonus as an ability modifier when attempting thieving skills.

Blinky the 1st-level thief tries to pick Mertrand’s pocket. This is a job for Blinky’s DEX, which he possesses as a primary attribute with a value of 11. The target number is 19 (base 16, +3 for Mertrand’s experience level). Blinky’s ability modifier is +4 (+1 for 1st-level, +3 for DEX 11 as primary). Blinky’s d20 roll must be a 15 or higher.

Bugby the 7th-level cleric decides he’s going to pick Blinky’s pocket. Again, this is a DEX check, and the cleric possesses DEX 14, though it’s not his primary attribute. Bugby’s target number is 17 (16, +1 for Blinky’s level) but his ability modifier is only +1 (+1 for DEX 14 and no level-based bonus). He needs an 16 or more to succeed.

Spell Casting
If you require spell-casters to roll when loosing a spell, the attribute check system is easily adapted. Assign magic spells to INT and clerical spells to WIS. Only classes capable of spell use may attempt spell-casting, and the spell level is added to the difficulty modifier.

Erol, the 2nd-level magic-user, needs to cast magic missile at a foe. Because the spell is 1st-level, the check’s TN is 17; Erol’s ability modifier is +6 (+2 for 2nd-level and +4 for INT 15 as primary). As a result, Erol needs a d20 result of 11 or better to cast the spell.

An interesting by-product of this approach is the opportunity it affords DMs to introduce various skills, components, and magic items that adjust the effectiveness of spell-casting attempts. For example, the Alternate Magics General Skill and rare spell ingredients might provide bonuses (to all or only certain spells). Similarly, a magic item might improve the caster’s ability (or, if cursed, hinder it completely).

Turn Undead
This ability remains entirely within the province of clerics and paladins, but is easily converted to the attribute check system. Attempts to turn are based on the cleric’s WIS score; the HD of undead targeted is added to the difficulty modifier. To determine the effects, subtract the minimum d20 result needed to succeed from the actual check result: the difference is the number of HD turned.The cleric’s alignment determines how turned undead react:

  • Lawful: Save vs. Paralysis (or STR) or disintegrate (failed save indicates retreat)
  • Neutral: Become inert, as if held, for 1 hour per cleric’s experience level
  • Chaotic: Save vs. Spells (or WIS) or serve the cleric as if charmed (failed save indicates inertia, as above)

Bugby the 7th-level cleric runs into a pack of zombies (2HD each). He holds up his holy symbol and attempts to turn the undead. This is a WIS check, and Bugby’s possesses WIS 16 as a primary attribute. His target number is 18 (16 +2 because of the zombies’ 2HD) but his ability modifier is a whopping +12 (+7 for 7th-level and +5 for WIS 16 as primary). He needs a 6 or more to succeed and rolls a 14, which means that 8HD [14 – 6 = 8] of zombies are successfully turned.

As with spell-casting, this option allows the DM to introduce items that influence the potency of turning. For example, a specially made holy symbol might impart a bonus of +2, or proximity to an evil alter might impose a difficulty modifier of +1 to turning attempts made by Lawful clerics.

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Erin Smale

Erin Smale is the author of the Chimera RPG and WelshPiper.com, a sporadic, rambling blog that provides tips and tools for the time-challenged game master. He lives in secret along the New Jersey coast with his ass-kicking wife Kim and astoundingly cute dog Bella.

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