Advantage-Disadvantage

The Advantage / Disadvantage mechanic
Advantage reflects the positive circumstances surrounding a d20 roll, while disadvantage reflects the opposite.

When you have either advantage or disadvantage, you 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 a 17 and a 5, you use the 5. If you instead have advantage and roll those numbers, you use the 17.

Advantage

 * If you have inspiration, you can expend it when you make an attack roll, saving throw, or ability check. Spending your inspiration gives you advantage on that roll.
 * Using a crowbar grants advantage to Strength checks where the crow bar’s leverage can be applied.
 * A magnifying glass grants advantage on any ability check made to appraise or inspect an item that is small or highly detailed.
 * A military saddle gives you advantage on any check you make to remain mounted.
 * When mounted – You have advantage on melee attack rolls against any unmounted creature that is smaller than your mount.
 * Helping another with a task (where your assistance could actually be of help) adds advantage to their check.
 * If you are hiding – “the Dungeon Master might allow you to stay hidden as you approach a creature that is distracted, allowing you to gain advantage on an attack before you are seen.”
 * When a creature can’t see you, you have advantage on attack rolls against it.
 * Attack rolls against a blinded creature have advantage.
 * Invisible creature’s attack rolls have advantage.
 * Attack rolls against paralyzed and petrified creatures have advantage.
 * An attack roll against a prone creature has advantage if the attacker is within 5 feet of the creature.
 * Attack rolls against restrained or stunned or unconscious creatures have advantage.

Disadvantage

 * If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity.
 * If the Armor table shows “Disadvantage” in the Stealth column, the wearer has disadvantage on Dexterity (Stealth) checks.
 * Small creatures have disadvantage on attack rolls with heavy weapons.
 * In lightly obscured areas – creatures have disadvantage on Wisdom (Perception) checks that rely on sight.
 * When attacking a target beyond normal range, you have disadvantage on the attack roll.
 * You have disadvantage when you use a lance to attack a target within 5 feet of you.
 * When you attack a target that you can’t see, you have disadvantage on the attack roll.
 * You have disadvantage on a ranged attack roll if you are within 5 feet of a hostile creature that can see you and that isn’t incapacitated
 * Blinded creature’s attack rolls have disadvantage.
 * Attack rolls against Invisible creatures have disadvantage.
 * Any level of exhaustion gives you a disadvantage on ability checks
 * A poisoned creature has disadvantage on attack rolls and ability checks.
 * A prone creature has disadvantage on attack rolls.
 * An attack roll against a prone creature has disadvantage if the attacker is more than 5 feet from the creature.
 * Restrained creatures have disadvantage on Dexterity saving throws and attack rolls.