Once again I’m quite late to the party, but I wanted to say how impressed I am with 5e’s new Advantage / Disadvantage mechanism. With all my tinkering over the years, I’m a bit surprised that nothing like it ever occurred to me.
What Is It?
Simply put, when you have advantage or disadvantage you roll two d20s instead of one. If you have advantage, you use the higher of the two rolls. If you have disadvantage, you use the lower of the two rolls. It is extremely straightforward and elegant. What isn’t as obvious is how powerful it is!
What Makes This So Powerful?
Normally, when you need to roll an 11 or higher on 1d20, you have a 50% chance of success. With advantage, your chance of success rises to 75%. With disadvantage, this chance drops to 25%. That is huge!
Here is a table showing the chance of rolling each DC (or higher) normally, and with advantage or disadvantage.
Isn’t a Static +5 Bonus or -5 Penalty Just The Same?
If you need to roll 11 or higher on 1d20, and have disadvantage, you still are shooting for an 11. If, instead of disadvantage, you received a -5 penalty, you now need to roll a 16. It “feels” harder to do and is discouraging. I realize that may seem silly to some of you, but we are playing a game in order to have fun. Making players feel discouraged should be avoided where possible. It is a subtle, but important, aspect of being a DM.
Furthermore, bonuses and penalties have no impact on crits and fumbles. If you have disadvantage, your chance of rolling a natural 20 drops from 1 in 20 (5%) to 1 in 400 (0.25%). Since you are taking the lower of the two rolls, both rolls must be a 20 in order to be considered a natural 20 (crit or potential crit depending on how you play). With disadvantage, there is roughly a 1 in 10 (9.75%) chance of rolling a natural 1 (fumble).
With advantage, there is roughly a 1 in 10 chance of a natural 20 (nearly twice as likely) and a 1 in 400 chance of a natural 1 (meaning you will almost never fumble).
It Is Simply More Fun!
Everyone loves to roll dice. When you have advantage or disadvantage you get to roll more dice. Good or bad, this makes the roll more of an event. It is something special and feels more fun. This is a game after all and having fun is the number one goal.
I love this mechanic! I wish I had thought of it. : )