Advantage is a dice mechanic that applies when a character is in a beneficial situation and increases a resolution roll's chance of success without affecting the range of possible results. Disadvantage is a similar mechanic that applies when a character is in an unhelpful position and decreases the chance of success. Both advantage and disadvantage are alternatives to other bonuses e.g. flat or stackable modifiers.
Advantage works by rolling an additional die of the same type used in a standard roll, then ignoring the result from the least beneficial die (most beneficial for standard disadvantage). Advantage is most often used in roll-over resolution systems (in which the least beneficial die will be the one with the lowest result), but can also be used in roll-under systems (in which the least beneficial die will be the one with the highest result) or keep-the-highest dice pool systems (although in these cases disadvantage will work differently, e.g. by removing dice from the pool).
Usage and probabilities
Advantage was popularised by its use in Dungeons & Dragons 5th edition, in which it is a central mechanic. Because resolution rolls in D&D are roll-over and use a single d20, rolling with advantage means rolling 2d20 and keeping only the higher result.
Whereas an ordinary d20 roll has a 5% chance of scoring any number in range, advantage skews the probability so that higher results are more likely: there is now a 9.75% chance of a natural 20 compared to a 0.25% chance of a natural 1. These probabilities will be precisely reversed when rolling with disadvantage.
The average impact is roughly equivalent to a flat modifier of +5 when the target number is close to 10, but the impact will be smaller for numbers further away from this. While a standard standard roll will have a 50% chance of scoring 11 or more (or, equivalently, 10 or less), rolling with advantage will have over a 50% chance of scoring 16 or more and rolling the disadvantage will have over a 50% chance of scoring 5 or less.
A number of Powered by the Apocalypse games, which typically use roll-over on 2d6 for resolution rolls, have adopted advantage mechanics inspired by D&D 5th edition. These include Legacy: Life Among the Ruins 2nd edition, Vagabonds of Dyfed, Spirit of '77 (in which advantage is called "roll with something extra" and disadvantage is called "roll with something less"), Voidheart Symphony, Hearts of Wulin, Fellowship, and Homebrew World.
In these games, an ordinary roll take the sum of 2d6. Rolling with advantage means rolling 3d6 and taking the sum of the highest 2 dice. Rolling with disadvantage means rolling 3d6 and taking the sum of the lowest 2 dice. 2d6 already produces a bell curve, which advantage and disadvantage skew higher or lower. The average impact is between the equivalent impact of a +1 flat modifier and a +2 flat modifier.
In Cartoon Action Hour, which uses a single d12 for its resolution mechanic, an advantage-like mechanic exists for characters with Traits beyond the normal human maximum, called super-ratings. The character's Trait rating is given as 4 (the maximum possible), with another number between 2 and 5 in parentheses. This second number indicates how many d12s should be rolled when testing that Trait, with the highest roll taken as the result.
For a super-rating of 2 (i.e. rolling 2d12 and taking the highest), there is a 75% chance of rolling at least 7 (11 after adding +4), compared to a 50% chance of 1d12 rolling at least 7 (11) and a 75% chance of 1d12 rolling at least 4 (8). A super-rating of 2 is therefore equivalent to roughly a +4 flat rating, effectively doubling a character's modifier (as +4 is already the maximum). A third d12 is equivalent to an additional +2 in the middle range (for a +6 total), and a fourth and fifth d12 roughly equivalent to an additonal +1 each in the middle range (up to an effective maximum of +8 in the middle range, without changing the maximum or minimum results).
Keep the highest
Other games that use an explicit advantage mechanic include TinyD6 system games (Tiny Dungeon, Tiny Frontiers, Tiny Supers, etc.). In these games, standard resolution rolls use 2d6 and only the highest contributes to the result. Advantage means that 3d6 are rolled instead, still keeping only the highest (equivalent to ignoring the lowest of the 3 rolls, as in roll-over games). However, disadvantage is no longer a symmetrical mechanic (add a die to the pool, ignore the best die result) but is now calculated by rolling only 1d6 instead of 2d6.
Advantage (particularly as used in Powered by the Apocalypse) also inspired the keep-the-highest dice mechanics in Blades in the Dark, and thus many other Forged in the Dark games, although unlike TinyD6 they generally do not use the term advantage to describe adding dice to the dice pool.
- "How does rolling two dice and taking the higher affect the average outcome?". At Role-Playing Games StackExchange. Retrieved 2020-01-17.
- "Advantage and Disadvantage in PBTA Games". The Gauntlet Forums. Retrieved 2020-01-17.
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