Roll-Over Hero System

I love Hero System for its engineering and its utility as a design toolkit.

I’m not so fond of the roll-under mechanism for task resolution. I was very happy when D&D 3e moved to a roll-over mechanism. This post explores what we can do to change Hero System to use a roll-over mechanism for task resolution.

Overall this should be pretty straightforward.

Task Resolution and Characteristic Checks

In Hero System, tasks are resolved by rolling 3d6 against a target number. The standard target number for many checks is ’11-‘ (rolling 11 or lower on 3d6). For trained skills the target is ‘9+CHA/5’ (9 plus the relevant characteristic divided by five… with ‘normal characteristics’ of 8..12, this is 11).

I’m changing the formula to CHA/5 – 2, so the human standard characteristic modifier is +0. This will make many things simpler (+0 is easier to add than +2, and more importantly we get to keep the target numbers reflecting properly — 11- becomes 10+, 12- becomes 9+, etc.)

Hero Roll-UnderRoll-Under NaturalNew Roll-OverRoll-Over Natural (+0 bonus)

For task resolution, it looks as though replacing the roll-under value with 21-rollUnder will give a roll-over target number with the same chance of success, once we remove the standard +2 modifier.

Easy tasks now have lower target numbers rather than higher target numbers, and any other modifiers (+3 for spending extra time, say) are simply added to the roll rather than adjusting the target number (or being subtracted from the roll).

Changing Characteristic Modifier

I got rid of the +2 modifier. Yes, this changed the formula a bit, but there are benefits.

  1. ‘Standard human characteristics’ will be +0 rather than have a modifier.
  2. In practice, +0 is easier than +2.
  3. This gives better symmetry when converting: 11- becomes 10+, 14- becomes 7+, and so on. If one is familiar with the 3d6 curve, this is very easy to equate.
  4. This will align better with changing combat to roll-over.

Combat (OCV vs DCV)

The instructions for determining whether or not an attack hits the target are

Attack Roll: Attacker’s OCV + 11 – 3d6 roll = DCV the attacker can hit

So, with an OCV of 2 and a roll of 11, we can hit DCV 2, a roll of 12 can only hit DCV 1. This is consistent with Hero System standard behavior, but I think we can do better.

If we change to

Attack Roll: 3d6 + OCV – 10 = DCV

we see a couple simplifications immediately.

  1. Changes from an awkward subtraction to a simple addition and subtraction.
  2. Can be made even easier if we precalculate part of it: ‘Dodge = 10 + DCV’, so it becomes 3d6 + OCV = Dodge (10 + DCV).

Uncontrolled Checks

When a character rolls a skill check, a characteristic check, or makes an attack, the character’s abilities make a difference. Characteristic scores (STR, OCV, etc.) affect the chance of success. I’m referring to these as ‘controlled checks’.

Uncontrolled checks are things the character has no control over. Activation checks for unreliable equipment, deciding if a particular disadvantage comes into play, and so on, these all ignore character ability.

In this case, keeping the ‘roll under’ mechanic helps highlight the difference.

Examples of When to Use Roll-Under vs Roll-Over

Spell requires a skill check to cast? Roll-over, It might be 10+ (with a -4 penalty for Active cost) or 14+ (with no penalty — precalculate it).

Wand has a loose crystal and doesn’t always work (Activation)? Roll-under. Flat 14- (it’s really loose).

Need to call on a Contact? Roll-under: the Contact either can or can’t help, and you can’t talk him into it.

Need to convince a (non-Contact) NPC to help you? Roll-over Persuasion check.

Critical/Automatic Success/Failure

Obviously the rules for critical or automatic success need to be inverted a well. A 3 is now the worst possible roll in a controlled check rather than the best, and 18 is the best instead of the worst. This likely aligns with most peoples’ expectations anyway, unless they’re accustomed to roll-under.

Closing Comments

It looks as though there are actually few places the rules really need to change. Task resolution, characteristic checks, and attack rolls make up many of the rolls in the game, but I think this post covers basically all the places that would be affected.

Addition and comparison are generally easier calculations than subtraction, and this reduces the number of calculations needed at the table because now many of the calculations can be done ahead of time.

It makes high rolls consistently better (modulo activation checks and the like): a roll of 14 on an attack will hit a higher DCV than a roll of 12.

(Not mentioned earlier, but it makes AGE-style stunt dice easier to incorporate, and that always pleases me.)


  1. Zak Sawyer

    I just stumbled across this randomly! Glad to see another HERO fan. I sort of went a different route than you and changed it to be a d% roll. Really neat to see how others have made changes though!

    • I really like Hero from an engineering perspective, but I’ve always found the play a little crunchier than I like, especially for a supers game. I’d really like to see an AGE System treatment, and I’m working toward that with these changes.

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