Hi all,
So I recently picked picked the starter set and ran the first part of the adventure. One of the things that came up was how to gain advantage/disadvantage, I saw a few things (Help action, hidden). I noticed that there doesn't seem to be many hard rules now for when to hand them out (ie flanking) outside of player abilities/spell that specifically call it out. Is advantage/disadvantage a thing that is mostly up to the DM to decide when it would be appropriate to use now? or did I miss some thing during my reading of the rules?
Thanks
Page 57, Basic Rules:
You usually gain advantage or disadvantage through
the use of special abilities, actions, or spells. Inspiration
(see chapter 4) can also give a character advantage on
checks related to the character’s personality, ideals,
or bonds. The DM can also decide that circumstances
influence a roll in one direction or the other and grant
advantage or impose disadvantage as a result.
So it's up to the DM if circumstances warrant advantage or disadvantage. In my games, I either state it as such up front ("It's disadvantage to attack rolls while on the slippery ice...") or players can earn advantage by paying a cost or taking a risk. I also reward voluntarily taking disadvantage on a check with Inspiration when the player ties it to a trait, bond, flaw, or ideal.
Having played a lot of 3.X, I would probably still award (and expect to be awarded) advantage while flanking, even though "flanking" doesn't appear anywhere in the 5E rules. Hopefully the Player's Handbook or (perhaps more likely) the Dungeon Master's Guide will spell this out more specifically.
As said above, the DM can decide that some circumstance not mentioned in the rules grant advantage or disadvantage.
You seem to be primarily concerned about advantage and disadvantage on attack rolls, which are advantage sources 6, 13, 15, 17, 18, 22-24, 28-36, and 38, and disadvantage sources 1, 2, 4-7, 9-15, 17-20, and 22-28 on the lists below. Conditions in particular (Basic p. 105) frequently give advantage or disadvantage on attack rolls.
In the Basic rules, the following grant advantage:
- Dwarven Resilience grants advantage on saving throws against poison.
- Elf Fey Ancestry grants advantage on saving throws against being charmed.
- Stout Halfling Stout Resilience grants advantage on saving throws against poison.
- Halflings’ Brave feature grants advantage on saving throws against being frightened.
- The Rogue Thief Archetype Supreme Sneak feature grants advantage on a Dexterity (Stealth) check if you move no more than half your speed on the same turn.
- Spending an Inspiration point (Basic p. 35) grants advantage on a single attack roll, saving throw, or ability check.
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Antitoxin: a creature that drinks this vial of liquid gains advantage on saving throws against poison for 1 hour. It confers no benefit to undead or constructs.
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Using a crowbar grants advantage to Strength checks where the crowbar’s leverage can be applied.
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A magnifying glass grants advantage on any ability check made to appraise or inspect an item that is small or highly detailed.
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One other character helping use a Portable Ram grants advantage on the strength check.
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Military saddles give the rider advantage on any check to remain mounted.
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A character working together can can make an ability check with advantage, reflecting the help provided by the other characters. In combat, this requires the Help action. A character can only provide help if the task is one that he or she could attempt alone.
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Under certain circumstances, 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.
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After three days of downtime spent recuperating, making a DC 15 Constitution saving throw allows you to choose choose one of two results, including for the next 24 hours, gaining advantage on saving throws against one disease or poison currently affecting you.
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Attack rolls against a creature squeezing into a smaller space have advantage while it’s in the smaller space.
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While using the Dodge action, you make Dexterity saving throws with advantage if you are not incapacitate and have nonzero speed.
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The Help action can also feint, distract a target, or in some other way team up to make your ally’s attack on a creature within 5 feet of you more effective. If your ally attacks the target before your next turn, the first attack roll is made with advantage.
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When a creature can’t see you, you have advantage on attack rolls against it.
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Beacon of Hope spell: for the duration, each target has advantage on Wisdom saving throws and death saving throws.
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Charm Person spell: if you or your companions are fighting the target, it has advantage on the saving throw.
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Dominate Monster spell: if you or creatures that are friendly to you are fighting the target, it has advantage on the saving throw.
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Faerie Fire spell: any attack roll against an affected creature or object has advantage if the attacker can see it.
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Foresight spell: for the duration, the target has advantage on attack rolls, ability checks, and saving throws.
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Guiding Bolt spell: on a hit, the next attack roll made against this target before the end of your next turn has advantage.
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Heroes Feast spell: Up to 12 other creatures that partake of the feast make all Wisdom saving throws with advantage for 24 hours.
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Holy Aura spell: targets have advantage on all saving throws until the spell ends.
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Haste spell: until the spell ends, the target has advantage on Dexterity saving throws.
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Otto’s Irresistible Dance spell: while the target is affected by the spell, other creatures have advantage on attack rolls against it.
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Shocking Grasp spell: you have advantage on the attack roll if the target is wearing armor made of metal.
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Attack rolls against a paralyzed creature have advantage.
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Attack rolls against a petrified creature have advantage.
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Attack rolls against a prone creature from within 5 feet of the creature have advantage.
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Attack rolls against a restrained creature have advantage.
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Attack rolls against a stunned creature have advantage.
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Attack rolls against an unconscious creature have advantage.
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Attack rolls against a blinded creature have advantage.
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The charmer has advantage on any ability check to interact socially with a charmed creature
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Invisible creatures have advantage on attack rolls.
In the Basic rules, the following cause disadvantage:
- Protection Fighting Style can impose disadvantage on a creature attacking a different target within five feet if you are wielding a shield.
- Wearing armor that one is not proficient in imposes disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity.
- Wearing some armor imposes disadvantage on Dexterity (Stealth) checks.
- Small creatures using heavy weapons have disadvantage on attack rolls.
- Ranged weapon attacks against a target beyond normal range have disadvantage on attack rolls.
- A lance has disadvantage on attack rolls against targets within 5 feet of you.
- The optional variant encumbrance rules give heavily encumbered creatures disadvantage on ability checks, attack rolls, and saving throws that use Strength, Dexterity, or Constitution.
- In a lightly obscured area, creatures have disadvantage on Wisdom (Perception) checks that rely on sight.
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While squeezing through a smaller space, a creature has disadvantage on attack rolls and Dexterity saving throws.
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While using the dodge action, any attack roll made against you has disadvantage if you can see the attacker and are not incapacitated and have a nonzero speed.
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When you attack a target that you can’t see, you have disadvantage on the attack roll.
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When you make a ranged attack with a weapon, a spell, or some other means, you have disadvantage on the attack roll if you are within 5 feet of a hostile creature who can see you and who isn’t incapacitated.
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When you make an underwater melee weapon attack, a creature that doesn’t have a swimming speed (either natural or granted by magic) has disadvantage on the attack roll unless the weapon is a dagger, javelin, shortsword, spear, or trident.
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When you make an underwater ranged attack, even against a target within normal range, the attack roll has disadvantage unless the weapon is a crossbow, a net, or a weapon that is thrown like a javelin (including a spear, trident, or dart).
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Blur spell: causes other creatures to have disadvantage on attack rolls against you. An attacker is immune to this effect if it doesn’t rely on sight, as with blindsight, or can see through illusions, as with truesight.
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Dream spell: if you have a body part, lock of hair, clipping from a nail, or similar portion of the target’s body, the target makes its saving throw with disadvantage.
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Foresight spell: other creatures have disadvantage on attack rolls against the target for the duration.
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Holy Aura spell: other creatures have disadvantage on attack rolls against targets of the spell until the spell ends.
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Otto’s Irresistible Dance spell: the target has disadvantage on Dexterity saving throws and attack rolls.
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Resurrection spell: after casting it to restore life to a creature that has been dead for one year or longer, you have disadvantage on all attack rolls, ability checks, and saving throws until you finish a long rest.
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Sunburst spell:, undead and oozes have disadvantage on the saving throw.
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A poisoned creature has disadvantage on attack rolls and ability checks.
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A prone creature has disadvantage on attack rolls and attack rolls from more than 5 feet away from the prone creature have disadvantage.
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A restrained creature’s attacks have disadvantage and it has disadvantage on Dexterity saving throws.
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A blinded creature’s attacks have disadvantage.
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A frightened creature has disadvantage on ability checks and attack rolls while the source of its fear is within line of sight.
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Attack rolls against an invisible creature have disadvantage.
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Level 1 of Exhaustion causes disadvantage on ability checks, and level 3 causes disadvantage on attack rolls and saving throws.
Thanks for all the replies. It helped quite a bit! 
Overpromises wrote:
@ Overpromises
Great list.
I will shamelessly steal it.
Thks
Overpromises wrote: