Arcanum Criticals

arcanum tim-cain game-design critical-hits combat rpg-mechanics

Abstract

Problem: How do critical successes and failures actually work under the hood in Arcanum: Of Steamworks and Magick Obscura?

Approach: Tim Cain dug through Arcanum's source code to trace every factor that feeds into the critical system — from skill checks to situational modifiers to outcome tables.

Findings: Arcanum's critical system is remarkably deep, touching every skill in the game (not just combat), with layered modifiers for lighting, awareness, range, status effects, magic/tech aptitude, training, fate points, and weapon-specific outcome charts. Critical failures can never drop below a 2% floor unless training bypasses the check entirely.

Key insight: Arcanum was the "everything and the kitchen sink" game — every idea anyone on the team ever had about criticals went in, producing a system far more granular than most players ever realize.

Source: https://www.youtube.com/watch?v=8g0aLMYxl4A

1. Skill Success: The Foundation

Before criticals can happen, a skill check must resolve. The base chance of success depends on:

  • Skill level — more ranks = higher chance
  • Training level — affects the roll
  • Range — for ranged skills, penalties apply based on distance, modified by the attacker's Perception
  • Obstacles — partial cover (bushes, non-solid fences) reduces success chance
  • Lighting — good lighting helps every skill except Sneak (which benefits from darkness). Creatures with night vision invert this
  • Awareness — if the target is unaware of you, skills like Stealth get a bonus. Sleeping targets give a flat +30 bonus to any skill used on them
  • Strength requirements — if your Strength is below a weapon's minimum, penalties apply
  • Status effects — blindness or crippled arms reduce success. Crippled legs specifically hurt Dodge. Paralyzed, stunned, prone, or sleeping targets give bonuses to the attacker
  • Skill-specific modifiers — Silence boosts Sneak, lock difficulty penalizes Lockpick, etc.
  • Magic vs. Tech dichotomy — using a magic item/spell on a tech target (or vice versa) introduces a flat chance to fail before the skill is even rolled

2. Critical Success Chance

Once a skill check succeeds, the game determines whether it becomes a critical success:

  • Proportional to skill — higher effective skill (after all modifiers) = higher critical chance
  • Magic items — some weapons increase critical chance on hits; some worn items increase critical chance on all skills
  • Situational bonuses — Master Sneak backstabs have a significantly higher critical chance
  • Called shots — the trade-off mechanic. Called shots lower your hit chance, but the same proportion that was subtracted gets added to your critical chance if you do hit. This is the entire reason called shots exist
  • Fate points — spending one gives an automatic critical success on whatever you choose
  • Bounds — the calculated critical chance can drop below 0 (never happens) or exceed 100 (always happens)

3. Critical Failure Chance

When a skill check fails, the game checks for critical failure:

  • Inversely proportional to skill — lower effective skill = higher critical failure chance
  • Damaged weapons — increase critical failure chance on attacks
  • Magic items — can increase critical failure chance, either as a weapon property or a worn item curse
  • Status effects — various effects raise or lower the chance
  • Tech items + magic aptitude — using a tech weapon when your aptitude leans magical introduces critical failure chance proportional to both the item's tech power and your magic aptitude
  • Dodge interaction — if a target critically succeeds their Dodge, it can cause the attacker to critically fail their hit (scales with training)
  • Fate points — the player can spend one to force an enemy to critically fail
  • Chain criticals — if a critical failure causes you to hit yourself or an ally, that hit is automatically upgraded to a critical hit
  • The 2% floor — critical failure chance can exceed 100% (guaranteed) but can never drop below 2%. One in 50 failures will always be critical. The only exception: if training explicitly says you never critically fail at a skill, the function is never called at all

4. Critical Effects

The outcomes of criticals are highly skill-dependent:

4.1. Critical Successes

  • Heal — can heal multiple crippled limbs at once (e.g., both arms in one use)
  • Disarm Trap — you recover parts from the trap
  • Combat — effects depend on the creature hit and the hit location. Head hits can knock unconscious; arm/leg hits can cripple the limb. Armor in the hit location can reduce these chances (e.g., helmets reduce knockout probability)
  • Training — higher training can force certain critical successes to always occur

4.2. Critical Failures

  • Lockpick — picks get jammed in the lock; only a key can unjam it
  • Pickpocket — you get caught
  • Heal — you fail and lose extra supplies (bandages, etc.)
  • Combat — determined by weapon-specific charts. Possible outcomes include: weapon takes damage or breaks, you hit yourself, you hit an ally, ranged weapons can misfire, some weapons explode, weapon gets dropped
  • Training — higher training can prevent certain critical failures from ever occurring

5. References