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:
        if q.state != "active": continue
        for obj in q.objectives:
            if obj.event == kind and matches(obj, data) and not obj.done:
                obj.count = min(obj.count + 1, obj.needed)
                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 once

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).
• Stacked buffs explode → percent modifiers multiplied together. Sum percents within a layer unless a rule says otherwise (refs §1).
• 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.
• World: level-design plus your engine's tilemap/3D skill (godot-tilemap, godot-3d-essentials).

References

• For stat/damage formulas, leveling curves, turn-vs-action combat timelines, inventory/equipment data shapes, and the quest state model, read references/stats-combat-quests.md.