Markdown

# Introduction

## The Core Rule

The twenty-sided die (d20) is at the heart of the action resolution mechanic. To make an attack, ability check, or saving throw, players roll a d20 and add their relevant modifiers. Apply any bonuses and penalties, and compare the total to the appropriate difficulty rating (Armor Class, Difficulty Class, and so on). If the total equals or exceeds the rating, the roll is a success. Otherwise, it’s a failure.

## Group Checks

Sometimes the Narrator will call for a group check. Group checks take place when the entire party is engaged in a single task.
In a group check, every player makes an ability check as described above. If more than half of the group succeeds in their check, the group as a whole succeeds. If half or less of the group succeed, the group as a whole fails.

## Criticals and Fumbles

When you roll a 20 on a d20 attack roll, saving throw, or ability check (before applying any modifiers, bonuses, and penalties), this is referred to as a “natural 20”. Rolling a 1 on a d20 attack roll, saving throw, or ability check (before applying any modifiers, bonuses, and penalties) is referred to as a “natural 1”.
Critical Hits and Fumbles. A natural 20 on an attack roll is a critical hit and is always successful. On the flip side, rolling a natural 1 on an attack roll is considered a critical fumble and always misses.
Critical Saves. A natural 20 on a saving throw is a critical save and always succeeds. A natural 1 on a saving throw is always a failure. When you choose to fail a saving throw, your result is a natural 1.
Critical Successes. A natural 20 on an ability check is a critical success so long as the creature attempting it would normally have succeeded on the check. On a critical success the objective of the check is achieved and something else happens as well.
Critical Failures. A natural 1 on an ability check is a critical failure so long as the creature attempting it would normally have failed on the check. On a critical failure, the objective of the check is failed, and something unfortunate happens as well.
Group Criticals. When making a group check, a critical success is achieved if all members of the party succeed in their checks, while a critical failure takes place if all members of the party fail.
Criticals and fumbles also provide opportunities for additional positive and negative consequences. At the Narrator’s discretion, a fumble might also result in a complication for the attacker.

# Advantage, Disadvantage, and Expertise

Some circumstances grant advantage or disadvantage on an ability check, attack roll, or saving throw. To make a roll with advantage or disadvantage, roll two twenty-sided dice instead of one. For advantage, you use the higher of the two die rolls. For disadvantage, you use the lower of the two. When you have both advantage and disadvantage (regardless of from how many sources), they cancel each other out and you roll normally.
Some class features or traits grant you an expertise die for an attack roll or saving throw, or in a specific skill or tool proficiency. When you make a d20 roll with which you have gained an expertise die, roll 1d4 and add the number rolled to the result of your check.
You can never roll more than one expertise die on the same roll. If another class feature or situation grants an expertise die of any size that applies to the same roll, you don’t gain another die; instead, the size of the largest expertise die increases by one step for that check, from 1d4 to 1d6, or 1d6 to 1d8. If you have a 1d8 expertise die on a check, further expertise dice have no effect.If you have advantage or disadvantage at the same time as an expertise die, only the d20 is rolled twice, not the expertise die.
While advantage is most commonly used to represent circumstantial factors affecting a situation, expertise dice typically represent the particular training a character takes into the adventure.