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Advantage and Disadvantage

Some situations are so favorable - or so unfavorable - that the system lets the dice show it. Advantage means you roll 2d20 and take the higher. Disadvantage means you roll 2d20 and take the lower. The mechanic shows up on attack rolls, ability checks, and saving throws - anywhere a single d20 matters.

This is the most-used "situational" mechanic in the compendium. Most training programs grant or remove it. Most pieces of gear that don't have a flat numeric bonus produce or counter it. Most conditions either confer it on attackers or impose it on the affected creature.

How To Roll

  • Advantage: Roll 2d20. Take the higher die. Add modifiers as normal.
  • Disadvantage: Roll 2d20. Take the lower die. Add modifiers as normal.

You add modifiers (ability mod, Proficiency Bonus, situational bonuses) after picking the die, not to both dice.

Stacking Rule

Advantage and disadvantage never stack with themselves. One source of advantage is exactly the same as five sources of advantage - you still roll 2d20 take higher, no more. Same for disadvantage.

If you have at least one source of advantage and at least one source of disadvantage at the same time, they cancel out completely - you roll a normal 1d20, no matter how many of each you stacked. There is no "net advantage" or "slight disadvantage." It is binary: advantage, normal, or disadvantage.

Example: Falke (DEX +3, trained in Assault Rifles, Proficiency +2) shoots at a militant (AC 14) who has been Slowed by a leg shot - that gives Falke advantage on the attack. But the militant is grappled with a friendly shooter, so Falke is also firing into melee - disadvantage. One source of each: they cancel completely. He rolls a flat 1d20 → 13, +3 +2 = 18 vs AC 14 → hit. Stacking three more sources of advantage on top would not have changed the roll - any disadvantage cancels any advantage.

Interaction With Crits

A natural 20 on either die under advantage still triggers a critical hit. A natural 1 on either die under disadvantage still triggers any "fumble" or natural-1 effect (e.g. firing into melee, certain weapon properties).

Under advantage you are roughly twice as likely to roll a 20; under disadvantage you are roughly twice as likely to roll a 1.

Interaction With Passive Checks

For passive checks (passive Perception, passive Investigation), advantage adds +5 to the score and disadvantage subtracts 5. They still don't stack: the swing is at most ±5.

Common Sources

There is no master list - the rule is "the GM names it" - but the recurring patterns are:

Advantage on you (good for you)

  • An adjacent ally is granting Help.
  • A target is Slowed, Restrained, or otherwise impaired against your attacks.
  • Several training programs (Awareness, certain Tactical, Combat Designation features).
  • The magnified optic tag on long-range Perception checks.
  • Surprise round, attacking from concealment, or other position-of-advantage scenarios.

Disadvantage on you (bad for you)

  • You are using gear you have no Training in.
  • You are Crouched targeting at long range, Shaken, Frightened, or Poisoned.
  • You are attacking through partial obscurement, smoke, or with Suppressive Fire on you.
  • You are firing into melee.
  • You are wearing armor with the "Disadvantage" stealth modifier and trying to be quiet.
  • You are off-hand in two-weapon fighting without the relevant Basic Training.

Disadvantage that disappears with the right Training Program

  • Most Training Programs' Level 1 effect is "remove disadvantage on X." This is the most common single Level 1 perk in the system. See Training Programs.

Compared to Classic D&D 5E

  • Mechanics are identical: 2d20 take higher / take lower, no stacking, any disadvantage cancels any advantage to a flat d20.
  • ±5 to passive checks works the same.
  • The sources are different in flavor - lots of optic tags, suppression, training-program toggles - but the math is unchanged.