Game Mechanics

The math behind Ultima I Unity: how damage, defense, difficulty, the Mondain duel, shops and leveling are actually calculated.

These are the actual numbers our reproduction runs on. Every formula is tagged with where it comes from. RNG(a, b) means a random integer from a up to but not including b, clamped to 255. Where a rule-set can be switched, the 1981 and 1987 versions are shown side by side, with any derived interpretation called out separately.

Selectable rule-sets (1981 vs 1987)

The toggles

Prototype design
  • Overworld Combat: 1981 Original or 1987 Remake (default 1987).
  • Dungeon Combat: 1981 Apple II or 1987 DOS (default 1987).
  • Weapon Availability: 1981 Original (shops sell the full town stock) or 1987 Remake (step-gated stock).
  • Spell Casting: Class Locked (1981, arcane spells stay Wizard-only) or Unrestricted (1987 remake, any class casts what it owns).
  • 1987 DOS Dungeon Armor Bug: optional toggle that reproduces the remake bug where worn armor gives no dungeon protection.
  • Space Docking: Precise (legacy pixel-perfect) or Assisted (a controller-friendly snap, an accessibility aid rather than an era setting).

Each toggle defaults to the behavior the prototype already used, so switching is opt-in. The 1981 sets are faithful transcriptions of the Apple II BASIC and community write-ups, not byte-exact executable dumps.

Weapon availability (1987 step-gate)

Community guide
Daggers to Rope & Spikes (1-4):  from the start
Sword, Great Sword (5-6):        at 1500+ steps
Bow, Amulet, Wand, Staff (7-10): at 3000+ steps
Triangle to Blaster (11-15):     never sold (steal or pond/pence drops only)

Steps count town and overworld moves only (dungeon moves are deliberately excluded). Under 1981 Original, shops sell whatever the town stock list holds, matching the prototype default. The step thresholds follow the gamercorner reference guide.

Core formulas (1987 default)