Gaming Rules-design note One Hero Engine

One Hero Engine: Core Rules

The core resolution rules for One Hero Engine, including checks, saves, tags, and the draft's general non-combat procedures.

Archived version: One Hero Engine v0.12 is an archived development draft. It is preserved for design history and is no longer the current rules version.

Return to the current One Hero Engine rules.

Attributes and modifiers

StatRole
STRStrength - Melee, grapples
DEXDexterity - Reflexes, stealth
CONConstitution - Endurance, poison
INTIntelligence - Lore, logic
WISWisdom - Willpower, awareness
CHACharisma - Presence, persuasion

Modifier Formula: (Stat - 10) / 2, rounded down

Skill checks

Skill checks use a roll-under mechanic:

  • Roll: 1d20; if the result is equal to or lower than your relevant stat (or stat + bonus/penalty), you succeed.
  • Apply Advantage/Disadvantage where relevant:
    • Advantage: Roll two d20s and take the lower result (since lower is better).
    • Disadvantage: Roll two d20s and take the higher result.

Important: Non-skill rolls (attacks, saves, etc.) use a “roll-over” system (d20 + bonus vs. Target Number). Always verify which system applies before rolling.

Saving throws

  • Roll: 1d20 + modifier.
  • Advantage: Apply if specialized.
  • Disadvantage: Apply when enemies have traits or abilities imposing it.
  • Spell Save TN: Equal to caster’s full stat score (e.g., INT 15 -> TN 15).
  • For non-spell saving throws, use a TN set by the GM, scenario, or encounter. Where the draft needs a generic difficulty benchmark, the published TN guide is Easy 6, Average 11, Hard 16, Legendary 20.

General resolution rules

All non-skill rolls (attacks, saves, etc.) use a “roll-over” approach: roll d20 + bonus vs. a Target Number. Skill checks, however, use a “roll-under” system.

Roll TypeDescription
OpposedBoth sides roll d20 + bonus; highest total wins (ties = Hero wins).
UnopposedRoll d20 + bonus vs. TN.
DifficultyTN
Easy6
Average11
Hard16
Legendary20

Advantage & Disadvantage:

  • Advantage: Roll 2d20; for roll-over tasks, take the higher; for roll-under tasks, take the lower.
  • Disadvantage: Roll 2d20; for roll-over tasks, take the lower; for roll-under tasks, take the higher.

Initiative

The current draft references acting order and even includes one ancestry trait that modifies initiative, but it does not publish a complete general initiative rule in v0.12.

Rules review required: The current source material does not define this procedure consistently.

Tags

  • Tags: Narrative keywords that describe your hero’s background and skills. They grant Advantage on appropriate rolls (whether using the roll-under or roll-over system).

Traits

  • Traits: Specific bonuses or abilities from your race, class, or progression. They can affect combat, magic, or narrative events.

HP and MP

  • MP = 5 + your casting stat modifier.
  • At the start of each new day (after an 8-hour long rest), a character automatically recovers 1d4 MP.
  • During a short rest or as a free action, you may choose to sacrifice a portion of your HP to recover additional MP.
  • For every 2 HP sacrificed, you recover 1 MP.

The current published draft references HP, healing, temporary HP, and HP sacrifice, but it does not define a full base HP formula or starting HP procedure in this rules article.

The current v0.12 draft also does not define a Hit Die or Hit Dice subsystem as a current core rule.

Rules review required: This procedure is not fully defined in the current published draft.

Rest and recovery

The current published draft explicitly defines:

  • Long rest: 8 hours; recovers 1d4 MP at the start of each new day
  • Short rest: may be used for HP-to-MP conversion

The draft also references short-rest healing or recovery in some class traits, but it does not define a full universal recovery procedure for HP, conditions, or other resources.

Rules review required: This procedure is not fully defined in the current published draft.

General scene and action flow

The current draft supports actions, narration, Oracle questions, and ongoing effects, but it does not define a complete non-combat scene framework separate from the turn structure and Oracle guidance.

Rules review required: This procedure is not fully defined in the current published draft.

End of article

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Solo RPG One Hero Engine Homebrew Rules