Sometimes a D20 Test is modified by Advantage or Disadvantage. Advantage reflects the positive circumstances surrounding a d20 roll, while Disadvantage reflects negative circumstances.
You usually acquire Advantage or Disadvantage through the use of special abilities and actions. The DM can also decide that circumstances grant Advantage or impose Disadvantage.
Roll Two D20s
When a roll has either Advantage or Disadvantage, roll a second d20 when you make the roll. Use the higher of the two rolls if you have Advantage, and use the lower roll if you have Disadvantage. For example, if you have Disadvantage and roll an 18 and a 3, use the 3. If you instead have Advantage and roll those numbers, use the 18.
They Don’t Stack
If multiple situations affect a roll and they all grant Advantage on it, you still roll only two d20s. Similarly, if multiple situations impose Disadvantage on a roll, you roll only two d20s.
If circumstances cause a roll to have both Advantage and Disadvantage, the roll has neither of them, and you roll one d20. This is true even if multiple circumstances impose Disadvantage and only one grants Advantage or vice versa. In such a situation, you have neither Advantage nor Disadvantage.
Interactions with Rerolls
When you have Advantage or Disadvantage and something in the game lets you reroll or replace the d20, you can reroll or replace only one die, not both. You choose which one.
For example, if you have Heroic Inspiration and roll a 3 and an 18 on an ability check that has Advantage or Disadvantage, you could expend your Heroic Inspiration to reroll one of those dice, not both of them.
Heroic Inspiration
Sometimes the DM or a rule gives you Heroic Inspiration. If you have Heroic Inspiration, you can expend it to reroll any die immediately after rolling it, and you must use the new roll. Heroic Inspiration can also be used to unlock Paragon Path abilities.
Limit: There is no limit to the amount of Heroic Inspiration you can have.
Gaining Heroic Inspiration: Your DM can give you Heroic Inspiration for a variety of reasons. Typically, DMs award it when you do something particularly heroic, in character, or entertaining. It’s a reward for making the game more fun for everyone playing.
Other rules might allow your character to gain Heroic Inspiration independent of the DM’s decision. For example, Human characters start each day with Heroic Inspiration.
