[RR] Advantage and Disadvantage Calculations

At Origins, I played in a couple of D&D 5th Edition playtest sessions, for a module and for the online tools. Two mechanics stuck out for me: the new system for preparing spells and advantage/disadvantage.

Advantage and disadvantage are simple to describe and powerful in their implications. If you have advantage, make the roll twice and take the higher number; if you have disadvantage, make the roll twice and take the lower number. Done.

3rd Edition had a similar intent with its “+/-2” default rule. If the DM was not sure what sort of bonus or penalty something imposed, just go with “2.” That is a 10% difference on a 20-sided die. How does “advantage” differ?

Quite a bit. Several people have run the numbers (I think “enumerate the 400 possibilities” is a better method than running a simulation). As noted, the effect of advantage is small at the extremes and huge in the middle. If you are nearly certain to succeed or fail, advantage is +1 or +2. If you have a 50/50 chance, it is +5. Out of 20, that is really, really big.

Players will also feel advantage and disadvantage very strongly because of the perceived gain/loss of the second die roll. If you roll two 18s, “eh,” you say, “advantage didn’t matter.” If you roll an 18 and a 2, that’s a success with advantage and a failure wit disadvantage, and you can see fate hanging in the balance of that mechanic. It’s a psychologically powerful factor.

: Zubon

3 thoughts on “[RR] Advantage and Disadvantage Calculations”

  1. I first saw the advantage rule in 4th Edition, which for some reason still doesn’t have a video game adaptation despite being arguably a stronger system for CRPGs than tabletop games. It feels very powerful, but I always suspected that when you ran the numbers it wouldn’t be too far off a +2 bonus. It feels like 5th ed’s version of 3rd ed’s trashing of THAC0, a change that feels so obvious that it makes previous editions feel clunky in retrospect.

    (I’m disappointed the repurposing of Endurance, Reflex and Will into essentially elemental resistances didn’t stick, although that feels like something that works better in a CRPG than it does in a tabletop game, where it’s a lot harder to roll for every AoE attack than it is to get every target to roll a defence.)

  2. The spell memorization system 5.0 is using showed up in an older game: Arcana Evolved. It was the game Monte Cook created after he departed Wizards in the wake of D&D 3.0 (pre 3.5, mind). It included a bunch of things they had talked about doing in 3.0 but felt they would be too off-putting for D&D traditionalists. One of them was the “Know X spells, Prepare Y spells from list X, cast Z times per day from list Y” mechanic. There were some differences (there were rules in place for “weaving” spell casting slots up or down. . . so one could spend three 2nd level slots to cast a fireball, or trade a 4th level slot for two l3rd level casts). I’ve been wanting someone to implement this system ever since I read it in Arcana Evolved (which I sadly have never been able to play).

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