Salt & Steel: Encounter Design

Document type: Design — Canonical
Status: Active Development
Last updated: 2026-04
See also: Monster Taxonomy | Boss Design | Naval Systems | World & Lore | Living Sea

Overview

An encounter in Salt & Steel is any moment in which the player and a hostile force engage. That definition is deliberately broad because the game's encounter design lives at the intersection of the monster taxonomy, the environment, the player's build, and the world's living state. The same creature family in different environmental conditions, with different modifier combinations, approached by different GURPS builds, creates dramatically different experiences.

This document defines how encounters are assembled, scaled, and varied — from the smallest pack of Common enemies to the procedurally generated world events of the Living Sea. The governing principle: no two runs through the same area should feel identical, but players who have mastered the systems should always feel their mastery expressed.

Part I: Encounter Composition

The Unit of Composition: The Encounter Group

Every encounter in Salt & Steel is assembled from an Encounter Group — a defined collection of enemies with specified roles:

Vanguard (1–3 enemies): The first to engage. Often the fastest enemies in the group. Their job is to pressure the player before the full group arrives. Vanguard enemies draw active defense responses before the player can assess the full threat landscape.

Core (3–8 enemies): The primary body of the encounter. Mix of melee and ranged, standard and modified. Core density determines the encounter's overall pressure level.

Specialist (0–2 enemies): Enemies with modifying functions — aura providers, summoners, ranged harassers, healers. Specialists are the highest-priority targets in any encounter; their effects change the threat profile of the entire Core.

Anchor (0–1 enemies): The heaviest, highest-HP enemy in the group. Often a Champion. The Anchor sets the encounter's duration — killing everything else while the Anchor persists keeps the fight alive. Anchors draw attention while Specialists operate.

Encounter Group Templates

Encounter Groups are generated from templates that define the rough composition. Templates are assigned to regions and enemy families; the specific enemies are drawn from the appropriate family pools.

Standard Pack (low-to-mid tier zones):

Vanguard: 2 Common enemies of a fast-moving type
Core: 4–5 Common enemies mixed melee/ranged
No Specialist or Anchor
Total: 6–7 enemies

Reinforced Pack (mid tier zones):

Vanguard: 2 Common enemies
Core: 4 Common + 1 Elite
Specialist: 1 Elite with modifier supporting the Core (e.g., a Common-supporting aura bearer)
No Anchor
Total: 7–8 enemies

Champion Pack (mid-to-high tier zones):

Vanguard: 2 Elites
Core: 3 Common + 2 Elites
Anchor: 1 Champion
No Specialist
Total: 8 enemies

Elite Formation (high tier zones):

Vanguard: 2 Elites
Core: 2 Elites + 2 Common
Specialist: 1 Elite with summoning or aura modifier
Anchor: 1 Champion with 3+ modifiers
Total: 8 enemies, heavily modified

Legendary Retinue (endgame zones, Legendary encounter):

Vanguard: 4 Elites (specifically chosen as the Legendary's lieutenants)
Core: None — the Legendary IS the core
Anchor: The Legendary itself
Flanking: 2 Champions positioned to split player attention
Total: 7 enemies, all significant threats

Role Specialization by Family

Different families naturally fill different roles in Encounter Groups:

Family	Natural Role	Notes
Pirates	Core (melee/ranged mix)	Captains = Anchor/Specialist
Imperial Soldiers	Core (formation), Anchor (Ironclad Marines)	Officers = Specialist (commanding)
Cultists	Specialist (chanters), Anchor (High Priests)	Sacrifice Deacons = high-priority Core
Sharks	Vanguard, Core	Never Specialist; purely aggressive
Ghost Pirates	Core, Vanguard	Phantom Bosuns = Specialist
Skeletal Crews	Core (volume)	Best as high-count swarms
Ironclad Sentinels	Anchor (Heavy Sentinels), Vanguard (Scouts)	Command Engine = Specialist
Deep Ones	Core (volume), Specialist (Depth Heralds)	Heralds = highest priority

Encounter Group Spacing

Encounters are spaced in zones according to zone tier and intended combat pacing:

Campaign zones: Groups spaced with 15–25 seconds of clear travel between them. Players should have moment of relative safety to assess resources, use flasks, plan the next engagement.

Mid-tier endgame zones: Groups spaced 8–15 seconds apart. Some overlap is intentional — groups adjacent to each other may merge into a larger encounter when the player triggers the second group before clearing the first.

High-tier endgame zones: Groups spaced 5–10 seconds apart. Intentional overlap is common. The expectation is continuous combat pressure.

Boss antechamber zones: Lighter encounter density than the zone itself, with a deliberate clear section before the boss arena. This is a breathing room design — the player should arrive at the boss with space to compose themselves, not while dodging the last pack.

Part II: Difficulty Scaling

The Two Scaling Axes

Encounter difficulty in Salt & Steel scales along two independent axes:

Area Level (the world's baseline difficulty): Every zone has an area level from 1 to 80. Area level determines the base stats of all enemies (HP, damage, resistances) on a continuous power curve. A level-40 enemy has roughly triple the effective HP of a level-20 enemy and deals more damage per hit. Area level is set by zone design and does not change between runs.

Encounter Quality (the modifier-driven variance): Area level establishes the floor. Encounter Quality — the rarity tier and modifier combination of enemies in a specific group — creates the ceiling. A high-area-level zone can generate extremely dangerous encounters when it rolls a Champion pack with synergistic modifiers, and more manageable ones when it generates standard packs.

The player's character level, build, and equipment determine where they fall on the difficulty curve. The goal: a well-built character at appropriate level finds the baseline experience engaging but not overwhelming, with Champion encounters providing genuine challenge and Legendary encounters requiring full attention.

Difficulty Modifiers: Zone-Level Adjustments

Players can modify the difficulty — and reward — of zones through the Nautical Chart endgame system. Modifiers are applied to maps before entering:

Quality Modifiers (increase monster stats):

Bloodied Waters — all enemies have 20% more HP, deal 15% more damage. Proportional loot increase.
Hunting Ground — enemy pack sizes increased by 25%. More enemies per encounter.
Elite Current — all Common enemies are upgraded to Elite; all Elite enemies are upgraded to Champion. Significant reward increase; significant difficulty increase.
Storm-Touched — a weather effect is active; affected by weather modifiers (see Part IV).
Infested — a specific creature family is dominant in this zone (e.g., "Infested by Deep Ones" means 60% of encounters use Deep One templates). Allows targeted farming of specific drops.

Boss Modifiers (affect specific boss encounters):

Awakened — the zone's boss has one additional phase. Reward: guaranteed Legendary-tier unique from boss's drop table.
Vanguard Escort — the boss has 2 Champion lieutenants that must be defeated before or during the boss fight.
Marked — the boss has 3 additional random Champion modifiers applied. Unpredictable behavior.

Voyage-Specific Modifiers: Each Voyage (seasonal period) introduces temporary modifier categories that reflect the Voyage's theme — a Voyage of the Eternal Storm makes Storm-Touched available at all tiers rather than high-tier only; a Voyage of the Sunken Empire introduces Drowned modifier lines that favor undead and aquatic encounter types.

Player-Side Scaling: GURPS Advantages in Encounters

The GURPS character system creates natural difficulty variance that is character-specific, not zone-specific:

Danger Sense: Characters with this Advantage receive a brief warning (0.5 seconds, audio tone and brief flash) before ambushes and hidden enemy triggers. This effectively removes the surprise-attack damage penalty for these characters, making ambush-heavy zones easier.

Combat Reflexes: Always acts first in initiative on the first round of any encounter. The Vanguard of an Encounter Group attacks second, not simultaneously with the character. Changes the dynamic of large encounters significantly.

Night Vision: Many high-tier zones use darkness as a difficulty modifier. Night Vision removes all darkness penalties. A character with this Advantage does not need to carry lanterns or light sources; zones designed around darkness mechanics become meaningfully easier.

High Pain Threshold: Injury penalties (accumulated from multiple hits) do not apply until a higher threshold. Large encounters where the player sustains multiple minor hits before being able to heal are less punishing for these characters.

These Advantages are build decisions — they cost character points — and they create genuine meaningful differentiation between characters of similar overall power levels. This is the GURPS depth expressed in encounter design: your character's identity changes the difficulty profile of encounters, not just your damage output.

Part III: Risk and Reward Balance

The Core Loop

Every encounter presents a risk/reward calculation:

Engage: Fight the encounter. Risk: HP loss, resource expenditure, potential death. Reward: loot, experience, crafting materials, progress.

Avoid: Navigate around the encounter without triggering it. Risk: missed loot and experience; some enemies will pursue if spotted. Reward: resource conservation.

Selectively engage: Fight the Champion and Legendary enemies while avoiding or rapidly clearing Common and Elite enemies. Risk: incomplete resource clearing. Reward: efficient loot-per-time ratio.

The game does not force a single approach. Avoidance is viable for players who have mastered navigation. Selective engagement is optimal for loot efficiency. Full clearing is rewarding for experience and crafting materials. Different GURPS builds may favor different approaches (a character with Stealth skill may prefer targeted engagement followed by stealth navigation; a Berserker-type may clear everything in their path).

Loot and Experience per Encounter Type

Encounter Type	XP Yield	Loot Yield	Crafting Materials
Standard Pack (no modifiers)	Low	Low (coins, common materials)	Common
Reinforced Pack	Low-Medium	Low-Medium	Common-Uncommon
Champion Pack	Medium	Medium-High (guaranteed rare)	Uncommon
Elite Formation	High	High (Champion drops + Elite drops)	Uncommon-Rare
Legendary Retinue	Very High	Very High (Legendary unique chance)	Rare
Boss (campaign)	Maximum for tier	Maximum for tier (guaranteed drops)	Boss-specific

Depletion and Restoration

Resources spent in encounters matter. Encounters are not isolated — they are part of a run through a zone, and the player arrives at later encounters with whatever they had after earlier ones.

Flask economy: Flasks refill on enemy kills at a rate that generally allows sustained engagement with appropriately-leveled content. High-difficulty modifiers reduce this — if enemies die slower, flasks refill slower.

Fatigue Points (for magical abilities): Magic-using characters draw on a finite resource. Encountering the zone's Legendary at low Fatigue means using it without full magical capacity. This is intentional — the late-encounter resource state is part of the difficulty of reaching the zone's end content.

Crew welfare: Ship-board encounters drain crew HP and morale. Crew members who take damage in naval encounter zones arrive at the next encounter slightly degraded. Long naval runs without port time deplete crew effectiveness.

The Risk Escalation of Modified Zones

When players apply quality modifiers to zones (Bloodied Waters, Elite Current, etc.), they are accepting a known risk increase for a known reward increase. The system must be transparent — the modifier's effects are displayed before entry, the reward estimate is shown, and the player makes an informed choice.

The design principle for modifiers: every modifier should feel like a meaningful trade, not a mandatory tax. Players should sometimes choose not to apply modifiers because the risk profile does not match their current build or resource state. A modifier that is always applied is not a choice; it is just a standard feature that should be part of the baseline.

Part IV: Environmental Encounters

The Living Sea pillar means the environment is not passive. Weather, terrain, and ecological systems create encounter conditions that exist independent of enemy design.

Weather Integration

Weather conditions are generated by the Living Sea server simulation and affect active combat zones:

Calm: No environmental effects. Full capability for all combat approaches.

Squall: -20% ranged accuracy for both player and enemies (wind deflects projectiles). Visibility reduced moderately. No structural damage. Adds a slight Unsteady modifier to open-ground movement.

Storm: -40% ranged accuracy. Visibility severely reduced. Fallen crew on ship decks is a hazard (Tripping terrain). Lightning strike chance on the highest elevated point in the zone every 30–60 seconds (predictable by audio cue 3 seconds prior). Enemies with weather-related behaviors (Storm Hawks, Thunderbirds, Storm Cultists) are enhanced: 25% increased damage, more aggressive attack frequency.

Fog Bank: Visibility reduced to 10 meters. Ranged combat at range greater than 10 meters is impossible. Ambush encounters are harder to avoid (see Part V). Naval combat in fog is close-range only. Some enemies (Ghost Pirates, Banshees, Fog Cultists) are enhanced in fog.

Hurricane: Extreme-condition event, rare and devastating. All movement on ship deck requires Wind Resistance checks (Strength-based skill roll every 5 seconds or be swept off deck). Ranged combat effectively impossible. Lightning strikes are frequent. Cannon fire is unreliable (wind deflection). The hurricane provides cover — enemies cannot effectively organize either. This creates chaos encounters where positioning and movement mastery matter more than damage output.

Night: Not weather, but a time condition that affects encounter behavior. Nocturnal enemies (Black-Maned Panthers, Storm Mourners, certain Ghost Pirates) are enhanced. Diurnal enemies (Storm Hawks, some humanoids) are less active. Players without Night Vision have penalty to spotting range for ambush threats. The aesthetic of the zone changes dramatically — bioluminescence becomes visible, lantern circles become the illuminated world.

Terrain Integration

Elevation advantage: Being above an enemy improves ranged accuracy (+10%) and reduces the enemy's melee reach. Being below reduces ranged accuracy (-10%). Terrain with elevation variance creates natural flanking positions and choke points.

Water terrain: Traversing water in on-foot zones applies movement penalty based on depth (shallow = slight penalty; deep = major penalty; enemies adapted to water have no penalty). Some abilities cannot be used in water (fire abilities, gunpowder weapons — a pistol fired while submerged simply will not fire). Water terrain also provides encounter type variation: aquatic enemies in the water are at their full capability; land enemies that enter water are degraded.

Chokepoints: Narrow passages force encounters into a specific shape. Enemies that rely on flanking (Jungle Cats, Smugglers) become less effective in chokepoints; enemies that rely on massed frontal pressure (Skeletal Crews, Drowned Sailors) become more effective. Encounter groups near chokepoints are designed with this in mind — the designers know a chokepoint is nearby and the encounter's composition accounts for how players will likely use it.

Destructible terrain: Certain environment elements can be destroyed during combat — barrel stacks can be ignited for AoE fire, rigging ropes can be cut to drop on enemies, unstable cave ceilings can be collapsed. These are not hidden options — they are telegraphed by visual signals (highlighted in the GURPS Danger Sense feedback system) and reward players who read the environment.

Flooding zones: Some dungeon areas flood during combat (triggered by boss abilities, tidal cycles, or environmental events). Flooding creates rising water terrain that applies growing movement penalty as the level rises. Aquatic enemies gain increasing advantage in flooding zones. The player has limited time before the zone is impassable by land-based tactics.

Ecological Triggers

The Living Sea's ecology creates encounter conditions that are not scripted:

Blood trail: A player who is Bleeding while traversing ocean-adjacent zones will attract Sharks from a wider radius and cause their attack frequency to increase. This is not a hidden system — it is an explicit design note in the Bleeding status effect's description. Players who prioritize healing Bleeding conditions in these zones are correctly reading the ecological threat.

Whale pod proximity: Whale pods occasionally pass through certain sea zones. Their presence causes large predators (Sea Serpents, Bull Sharks) to surface — drawn by the same resource concentration the whales represent. This can create unexpected encounter additions to zones with whale migration paths.

Night creature emergence: After dark, the surface of the sea in open ocean zones changes its encounter table. Bioluminescent creatures come to the surface. Certain Eldritch entities are more active. The Deep Ones patrol the surface. Night zones feel fundamentally different from day zones despite sharing the same space.

Part V: Ambush Mechanics

Salt & Steel's world contains enemies that do not wait for the player to approach them. Ambush mechanics reward environmental awareness and character investment in perception-type Advantages.

Ambush Types

Standard Ambush: Hidden enemies triggered by player proximity. Enemies are concealed in foliage, water, or shadow and emerge when the player enters their trigger radius. The trigger radius varies by enemy type — Crocodiles trigger at close range; Jungle Runners trigger from further away and attack before the player reaches them.

Counter: The Danger Sense Advantage triggers a 0.5-second warning before emergence. High Perception skill increases the visual detection radius so players can spot concealed enemies before they trigger. Moving slowly (reduced movement speed) reduces trigger radius for many ambush types.

Visual tells: Most concealed enemies have subtle tells — ripples in still water for Crocodiles, swaying foliage where there is no wind for Jungle Cats, an absence of other ambient creatures (birds, insects) near a concealed predator. These tells are consistent enough that players who learn them can read most ambushes.

Attack Ambush: Enemies positioned above or behind the player's approach path who attack before the player can establish facing. Humanoid enemies (Smugglers, Pirates, Soldiers) use this — they know the player is coming and set up a kill zone.

Counter: Approach sound alerts (slower movement on stone/sand is quieter; running on gravel/wood is loud). High Tactics skill (or Streetwise for human enemies) provides a brief tactical view of obvious ambush positions before entering a new area. The Danger Sense Advantage provides warning for this type as well.

Design principle: Attack ambushes should teach players to clear elevated positions before advancing, to check behind cover, and to be suspicious of obvious choke points. Dead ends should have exits — a room with one entrance and concealed enemies is a legitimate challenge, not a trap with no agency.

Spawn Ambush: Enemies that spawn in behind the player after they have passed a trigger. The player is engaged with enemies ahead and new enemies emerge behind them.

Counter: Sound design — spawning enemies have distinctive audio cues (a splash for aquatic spawns, a creak for ghost ships spawning ghost crew, a ground tremor for buried crabs). The player who hears this cue immediately knows to change defensive orientation.

Design restriction: Spawn ambushes must never spawn enemies behind the player in positions that block retreat from the forward engagement. Players must always have a direction they can move toward. Trapped encounters (enemies in front and behind with no viable movement option) are acceptable only for designed set-pieces, never as random generation output.

World Event Ambush: The Living Sea generates emergent ambush situations — a pod of whales that has attracted a Sea Serpent the player does not know about; a distress signal that is a lure from a pirate crew; a fog bank that conceals a fleet of ghost ships. These are not scripted; they arise from world simulation state.

Counter: Reading world signals. A player who knows that whale pods attract predators investigates before sailing into the pod. A player who reads the captain's reputation (certain reputation values make lure-traps more common) takes distress signals with appropriate skepticism. The GURPS Empathy Advantage provides a social tell for human-set lures — an NPC "in distress" reads wrong.

Ambush Difficulty Scaling

Ambush frequency and sophistication scale with zone tier and applied modifiers:

Campaign zones: Ambushes are common but signposted — the level design places them in locations where players who are exploring carefully will notice the tells. The first ambush a player encounters in each new environment type is made obvious so the pattern registers.

Mid-tier endgame zones: Ambushes are more subtle. Tells are present but smaller. The player needs to be actively looking, not just passively walking through.

High-tier endgame zones with Infested or Elite Current modifiers: The dominant creature family may use ambush as its primary combat initiation. A zone infested by Jungle Cats is an almost continuous ambush experience. The modifier's description warns players what to expect.

Night conditions: All ambush trigger radii reduce by 30% (enemies can hide more effectively), and tells are harder to read in reduced visibility. Characters without Night Vision face significantly more ambush risk at night.

Part VI: Procedural Encounter Generation Rules

The encounter generation system creates variety across every run through the same zone without making that variety incomprehensible. Rules that govern it:

Generation Principles

Rule 1: Family consistency per area. Each area's encounter generation draws from a primary family pool (2–3 families) and a secondary family pool (1–2 families). Primary families appear in 70% of encounters; secondary families appear in 30%. This ensures zones feel ecologically coherent — the Jungle of Santa Catalina is a Jungle Cat / Native / Boar zone, not a random selection from all 32 families.

Rule 2: Modifier weights by zone tier. Low-tier zones weight toward defensive and movement modifiers (Shielded, Hasted). High-tier zones add aggressive modifier access (Berserking, Vampiric, Temporal Bubble). Endgame zones have full modifier access. This ensures difficulty escalation feels smooth rather than jarring.

Rule 3: Synergy ceiling. The generation system has a maximum allowed synergy score — a numerical representation of how well an encounter's modifiers work together. Synergies above a threshold are rerolled. This prevents the game from generating encounters that are mechanically impossible for appropriately-leveled characters. Note: Champions with maximum modifier stacks can still approach this ceiling; the ceiling exists to prevent exceeding it, not to eliminate challenge.

Rule 4: Specialist rationing. At most one Specialist per Encounter Group (except in specially designed high-tier templates). Multiple simultaneous Specialist effects compound unpredictably and create encounters that read as unfair rather than difficult. Two simultaneous healers that keep an entire pack alive indefinitely is a design failure; one healer that must be prioritized is a tactical problem.

Rule 5: Anchor confirmation. Every encounter with a Champion or Legendary Anchor gives the player a brief (0.5 second) visual signal before the Anchor reveals itself or before the encounter begins. Not a full telegraph — just enough that the player knows something significant is in this encounter before they are committed. This preserves the surprise of the Anchor's specific modifiers while ensuring the player is not surprised to be in an Anchor-tier encounter.

Rule 6: Encounter separation integrity. The generation system maintains minimum separation distances between encounter groups. Two Champion Anchors cannot spawn in adjacent encounter groups (they would merge into a single difficult encounter). Two Specialists of the same type cannot appear within three encounter groups of each other (the same modifier effect twice in quick succession reduces variety). Separation integrity ensures the pacing remains varied rather than clustered.

Rule 7: Legendary encounter rate. Legendary enemies spawn at a rate of approximately one per complete zone run at base rate, potentially two with appropriate map modifiers. They are not common enough to feel routine; they are common enough that a full zone run reliably contains a meaningful named encounter. The Legendary's specific identity is randomly selected from the pool appropriate to the zone's primary family.

Special Generation: The Wandering Named

In addition to the standard Legendary-per-zone rate, the world contains a pool of Wandering Named enemies — Legendary-tier entities that can appear in multiple zones and carry persistent tracking. The Pale Deacon (the ancient White Shark) can be encountered in any open-water zone in the Pale Waters region, not just one specific map. The Elder of the Deep Woods can appear in any high-tier jungle zone.

Wandering Named have the same ability sets and drops regardless of which zone they appear in. They appear to players with appropriate world flags (reputation level, zone completion status). Their appearance is a guaranteed meaningful encounter regardless of which zone the player is running.

Special Generation: Emergent Escalation

If a player spends an extended time in a zone (measured by kills rather than time), the encounter generation system escalates. This prevents indefinite farming of easy encounters without consequence:

At 150% of expected zone kills: all remaining Common encounters upgrade to Reinforced Pack templates.
At 200%: all Reinforced Packs upgrade to Champion Pack templates. The zone is now at heightened alert.
At 300%: The zone generates a unique warning event — a drumbeat (humanoid zones), a rising tide (aquatic zones), a gathering darkness (supernatural zones) — followed by a Legendary encounter that is flagged as "Escalation Response." This is a harder, modified version of a standard zone Legendary.

Escalation Response encounters drop at increased rates from the zone's Legendary pool and always include a special material unique to the escalation event. They reset the kill counter.

This system rewards extended farming with escalating difficulty and reward, and ensures that every zone has a ceiling that provides genuine challenge for players who push it.

Part VII: Naval Encounter Composition

Naval encounters follow parallel rules adapted to the naval combat layer:

Naval Encounter Groups

Standard Patrol: One enemy ship, standard armament, standard crew. The baseline naval encounter.

Convoy: 1 merchant ship + 1–2 escort warships. The merchant ship is the loot target; the escorts are the combat threat. Prioritizing escorts allows the merchant to flee but reduces combat pressure; engaging the merchant first prevents escape but leaves the escort free to attack.

Fleet Formation: 3–5 ships operating in coordinated formation. Each ship has a designated role (vanguard fast sloop, broadside frigates, command flagship). Disrupting formation (sinking the vanguard, disabling the flagship) causes the formation to break, changing the encounter's tactical landscape.

Sea Monster + Panic: A sea monster has attacked shipping in a zone; the player encounters both the monster and the damaged ships (enemy, neutral, or allied depending on zone faction state) simultaneously. The monster attacks both the player and the ships. Creating cross-fire situations is possible.

Naval Encounter Scaling

Area-level equivalent for naval zones is the sea region's naval combat tier (1–10). Each tier adds:

Ship HP multiplier (each tier adds 15% base ship HP to all enemies)
Armament tier (higher-tier zones have enemy ships with larger, more numerous, better-operated guns)
Crew quality (higher-tier crews are more accurate, faster to reload, more resistant to crew-damage tactics)

Naval encounter quality modifiers:

Hardened Hull — enemy ships have 40% more hull integrity
Elite Crew — enemy crew fires 30% faster with 20% better accuracy
Coordinated Fleet — fleet formation ships are perfectly coordinated (no lag between order and execution)
Cursed Vessel — the ship has supernatural properties (Ghost Ship: partially immune to physical cannon damage; Fire Ship: on death, engulfed in magical fire that spreads to adjacent ships)

See also:
Monster Taxonomy — The families and modifier system that populate encounters
Boss Design — Encounter design at the boss tier
Naval Systems — Naval encounter implementation
Living Sea Pillar — The world simulation that generates environmental encounter conditions
GURPS Framework — How Advantages and Skills interact with encounter difficulty