2E ADV/DIS - Advantage & Disadvantage is a polished Fantasy Grounds Unity extension for the official AD&D 2nd Edition (2E) ruleset. It brings the modern, intuitive Advantage/Disadvantage mechanic (roll the die twice, keep the favorable result) to all four major roll types: attacks, saving throws, ability checks, and skill checks—including full support for percentile (d100) rolls. It also modernizes the modifier stack for better usability.

Core Features

• Advantage/Disadvantage on Every Roll Type: Click ADV or DIS before any attack, save, ability check, or skill check. The engine rolls two dice and keeps the better (or worse) result, with both dice shown in chat—the dropped die greyed out and the kept one clearly tagged [ADV] or [DIS].
• Smart Roll-Under Handling: 2E ability and skill checks are roll-under (lower is better). This extension correctly keeps the lower die on Advantage for those rolls, while attacks and saves (roll-over) use the standard higher-die logic. Percentile checks (including reverse % like open doors) are fully supported using the same consistent approach.
• Modernized Modifier Stack: Replaces 2E’s original 10-button layout with a cleaner 8-button design:
  • ADV / DIS (first, wider 5E-style buttons for easy access)
  • +1 / -1, +2 / -2, +3 / -3, +5 / -5
  • +4 / -4 intentionally removed for a streamlined experience. Buttons are draggable to hotbars just like stock modifiers.

Technical Implementation (Clean & Extensible)

This extension is purely additive—no stock 2E ruleset files are edited. It hooks into CoreRPG’s generic wildcard extension points (onActionPreModRoll and onActionPreOnRoll via GameManager.setMultiKeyFunction).

• Leverages existing CoreRPG code (ActionD20.encodeAdvantage / decodeAdvantage) for the actual roll-twice-and-compare logic. This works seamlessly for both d20 and d100 dice.
• Includes defensive logic for future compatibility with a planned Target 20 extension (checks Target20Manager.isActive()—harmless if not installed).
• Carefully handles 2E’s roll-under mechanics without breaking ModifierManager key consumption or chat output.
• Scoped to single d20 or d100 rolls for safety and correctness. It gracefully does nothing (and releases the button) on 3d6/4d6 ability check modes from the “AD&D Options and House Rules” extension.

Usage

1. Load the extension in a 2E campaign.
2. Open the Modifier Stack—the new ADV/DIS buttons appear prominently.
3. Toggle ADV or DIS (or drag to hotbar).
4. Make your roll as usual. Chat shows both dice with clear visual feedback.
5. Works on PC sheets, NPC actions, and all standard 2E roll flows.

Layout Notes: ADV/DIS buttons use wider sizing for readability. Anchor adjustments ensure clean positioning alongside the remaining numeric modifiers.

Compatibility

• Official AD&D 2nd Edition ruleset.
• Compatible with “AD&D Options and House Rules.ext” (including 3d6/4d6 ability checks—does nothing safely in those modes).
• Composes well with other 2E extensions (including the planned Target 20).
• Pure extension hooks—no ruleset overwrites.