My AD&D Mods

tim-cain ad&d house-rules modding game-design system-design tabletop flaws economy clerics

Abstract

Problem: How did a teenage Tim Cain approach modifying AD&D's rules, and what design lessons emerged from decades of house rules?

Approach: Tim walks through four major modifications he made to his high school AD&D campaign, stored in repurposed California Power and Light Company orientation manuals, explaining what worked, what failed, and why.

Findings: The most successful mods added meaningful character differentiation (deity-based cleric abilities), while mods that added realism without fun (falling damage tables, economic taxation) were eventually dropped. Random character mutations (proto-advantages/disadvantages) were engaging but too unbalanced to sustain.

Key insight: Modding existing games — tabletop or digital — is the lowest-barrier way to explore design ideas, and the instinct to modify systems is the same instinct that makes good game developers.

Source: https://www.youtube.com/watch?v=58m_uEm-dBs

Context: Tim Cain on Modding

Tim opens by endorsing modding as both a hobby and a career strategy. He notes that Obsidian hired someone for The Outer Worlds based on a Skyrim mod — the mod moved his resume to the top of the pile. For aspiring developers, modding an existing game to demonstrate a cool feature is a perfectly valid demo.

Tim played AD&D for roughly 20 years (high school through early Interplay) and kept all his campaign materials in repurposed industrial manuals his mother brought home from her work at the Judge Advocate General's office.

Standard House Rules

Before getting to his major mods, Tim lists the common-sense changes his group made:

  • 4d6 attribute generation (drop lowest) — the optional method from the DMG
  • Removed the 18/50 Strength cap for women — his graduate school group told him it was a dumb rule
  • Reroll characters with multiple attributes below 6 — since the rules implied you could only be one class with a sub-6 stat, having two was unplayable
  • Dropped the grappling rules — complicated and nonsensical
  • Dropped the weapon vs. armor type chart — impossible to determine the "base armor type" of non-humanoid creatures (what's a dragon's base armor type when the chart only goes down to AC 2?)

Mod 1: Character Mutations (Proto-Flaws System)

At character creation, players rolled percentile dice. On a 96-99, they rolled once on a mutation table; on 00, they rolled twice. Results ranged from Major Malevolent to Major Benign:

  • Good results: Regeneration, ultravision, infravision
  • Bad results: Deafness, blindness, attribute loss, hemophilia

Tim explicitly notes this predates him ever seeing GURPS by at least a decade, but it's essentially a poorly balanced version of GURPS advantages/disadvantages — no bonus for taking a penalty, no penalty for getting a bonus.

The Death of the System

Tim's friend William rolled double zeros (two Major Malevolent results): his character was blind and had hemophilia (bleeding from any cutting/impaling damage until fully healed). William didn't even try to survive — the character died in the first battle intentionally. The table was retired shortly after.

Tim reflects that this was arguably his first experiment with what would become the perks/flaws system he later explored professionally, at age 14.

Mod 2: Deity-Specific Cleric Abilities

This was the most popular and longest-running modification. Every character had to pick a god (Tim maintained comprehensive charts by class, alignment, and race). Clerics received a unique ability and a unique restriction from their deity:

Example: Clerics of Astoreth

  • Ability: One undetectable lie and one Phantasmal Force per day
  • Restriction: 5% cumulative chance per level of becoming a pathological liar (always lies, never tells truth)
  • Ability: See through illusions/disguises (same chance as a thief's pickpocket skill minus disguiser's level); two clerics could communicate 25 words with no range limit if one knew the other's general whereabouts
  • Restriction: Must hide temples in every country except their homeland; must burn all waste products from their body, including hair

Tim's friend Joel played an Aura cleric for a long campaign run. He kept a pit of green slime in his temple basement to dispose of his waste products daily. The restrictions created emergent roleplaying that made clerics — and their players — far more interesting.

This system predated D&D 3rd Edition's domain-based cleric design by years.

Mod 3: Economic Taxation System

To control the money supply, Tim implemented a comprehensive taxation system:

  • Level-up cost: 1,500 gold × current level
  • Import duties: 1% on goods entering a city (5% for luxury goods), higher for foreign citizens
  • Entry fees: Based on heads and wheels (a cart with a donkey = 2 heads + 4 wheels)
  • Annual taxes, sales taxes, property taxes
  • Religious tithe: 10 gold/month + mandatory church attendance, or no healing/resurrection services
  • Foreign currency exchange fees
  • Higher taxes on gems and jewelry
  • Guild dues: 100 gold/level/month (but guilds provided benefits — Fighter guilds gave cheap mercenaries, Thieves' Guild gave black market access and lockpicks)
  • Toll roads

Why It Was Dropped

It worked — money stayed in check — but the bookkeeping was exhausting to do by hand. Tim notes this would be trivial in a computer game but was miserable on paper. A clear case of a mechanically sound system killed by implementation friction.

Mod 4: Detailed Falling Damage

The standard D&D rule (1d6 per 10 feet past the first 10) felt too generic. Tim's replacement used percentile dice per 10-foot increment, with results ranging from reduced damage to increased damage (d8, d10, d12), plus chances of sprains and broken bones requiring either:

  • Rest at an inn (which costs money — tying back to the economy system)
  • Temple healing (which requires active tithing)

Why It Was Dropped

Tim calls it "a form of realism that wasn't fun" — referencing his separate video on that topic. The interconnection with the economy system was elegant in theory but punishing in practice.

The Throughline: Modding as Design Education

Tim's closing argument ties everything together: he played AD&D unchanged for a few months, then spent years modding it. This progression — learn the system, then modify it — is natural and healthy for any game. Board games get house rules (everyone had Monopoly house rules as kids), and video games should get mods.

For aspiring designers, modding offers idea exploration with an extremely low barrier to entry: the engine and art already exist. You're free to focus purely on the design question you want to answer.

References