/rpg

name: rpg
description: >
  Build an RPG: stats and leveling, inventory and equipment, quests, branching dialogue, save/load,
  and combat. Use for an RPG/JRPG, or designing stat, inventory, quest, or combat systems.

RPG

A playbook for role-playing games — stats and progression, inventory/equipment, quests, dialogue, and combat. This is a **compositional** skill: it ties data-driven content, dialogue, and saving together. It does not re-teach those primitives; it defines the systems that make growth and choice feel meaningful, and points to the skills that implement each.

When to use

• Use when building an RPG/JRPG/action-RPG: the player has **stats that grow**, an

**inventory**, **quests**, **dialogue**, and persistent progress.

• Use when designing a leveling curve, a damage formula, an inventory/equipment model, or a

quest state machine.

**When *not* to use:** permadeath dungeon runs with no persistent character → `roguelike`. Pure conversation/branching story → `visual-novel`. Open-world needs/crafting/base-building → `survival-crafting`. For the dialogue engine itself, use `dialogue-systems`.

Core loop

**Explore → encounter (fight / talk / solve) → earn rewards (XP, loot, story) → grow (level up, gear up, unlock) → take on harder content.** The fantasy is *getting stronger and shaping who your character is*; every system should feed that growth-and-choice loop.

Must-have systems

1. **Stats + leveling** — base attributes, derived combat stats, XP curve, level-up gains. 2. **Inventory + equipment** — data-defined items, stacking, slots, stat modifiers. 3. **Combat** — turn-based or action; damage formula, status effects, win/loss. 4. **Quests** — objectives, state machine (available→active→complete→turned-in), rewards. 5. **Dialogue** — branching lines, conditions on game state, choices that matter. 6. **Save/load** — persist character, inventory, quest progress, world flags, with versioning. 7. **Economy + progression gating** — gold/shops; gate power behind level/quest/region. 8. **UI** — HUD, inventory, quest log, dialogue box, character sheet.

Design knobs

| Knob | Effect | Notes | |------|--------|-------| | XP curve shape | pacing of power | Fast early, slow late (see refs). | | Stat→derived scaling | build diversity | One attribute shouldn't dominate. | | Damage formula | tactical feel | Subtractive vs. ratio mitigation (refs). | | Random variance / crit | swinginess | ±10% and ~1.5× crit are safe defaults. | | Drop rates / economy | reward cadence | Avoid trivializing shops with loot. | | Power gating | difficulty gating | Level/region/quest locks. | | Reversible modifiers | buff/gear correctness | Layer mods; never edit base stats. | | Choice consequence | role-play weight | Quest/dialogue flags should branch outcomes. |

Patterns

1. Derived stats from base attributes (recompute, never store as truth)

# Pseudocode. Base attributes are the only "truth"; combat stats are derived each time.
def derive(base, mods):
    s = apply_modifiers(base, mods)          # base + flat adds + percent, then clamp
    return {
        "max_hp":  20 + s["VIT"] * 8,
        "attack":  s["STR"] * 2,
        "defense": s["VIT"] + s["AGI"] * 0.5,
    }
# Equipping pushes a modifier; unequipping pops it. HP/attack recompute automatically.

2. XP curve + level-up

# Pseudocode. Quadratic curve: fast early levels, long late ones.
def xp_to_next(level, base=100): return base * level * level

def gain_xp(actor, amount):
    actor.xp += amount
    while actor.xp >= xp_to_next(actor.level):
        actor.xp -= xp_to_next(actor.level)
        actor.level += 1
        actor.base["STR"] += 2; actor.base["VIT"] += 2   # grant gains / skill points
        on_level_up(actor)                                # heal, unlock, notify

3. Quest objective update driven by game events

# Pseudocode. Game events advance matching objectives; completion grants rewards.
def on_event(kind, data):
    for q in active_quests:
        for obj in q.objectives:
            if obj.event == kind and matches(obj, data) and not obj.done:
                obj.count += 1
                if obj.count >= obj.needed: obj.done = True
        if all(o.done for o in q.objectives):
            q.state = "complete"                # turn-in grants xp/gold/items

Pitfalls / failure modes

• **Editing base stats for buffs/gear** → values drift and corrupt on save/reload. Keep a

modifier layer; push/pop it (Pattern 1).

• **Storing derived stats as truth** → desync after a stat change. Recompute from base.
• **Runaway XP/damage numbers** → either an exponential curve with no cap or a subtractive

formula at huge values. Pick a curve and a formula family deliberately (refs).

• **Content as code** → every item/quest hardcoded. Define items, enemies, and quests as

**data** (`godot-resources` / `unity-scriptableobjects`).

• **Save format with no version field** → old saves break on update. Add a `version` and a

migration path from day one (see `save-systems`).

• **Choices without consequences** → dialogue branches that reconverge immediately feel hollow.

Set flags that actually change later quests/world state.

• **Quest progress not persisted** → reloading loses mid-quest state. Save quest state, not

just completion.

Composition (build it from these skills)

• **Dialogue:** `dialogue-systems` (Yarn Spinner / Ink) — branching lines, conditions, variables.
• **Persistence:** `save-systems` — character, inventory, quest flags, world state, versioning.
• **Content data:** `godot-resources` / `unity-scriptableobjects` — items, enemies, quests, skills as assets.
• **Combat AI:** `game-ai` for enemy behavior; for turn order reuse the scheduler idea in `roguelike`.
• **UI:** `game-ui-ux` for HUD/menu layout, resolution scaling, and controller/keyboard nav; `godot-ui-control` for the concrete inventory, quest log, character sheet, and dialogue box.
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