Attacks and spells require line of effect to a target or point of origin. But what about other effects like class features, magic items, and monster actions? Will a divination wizard's Portent or an Allip's Whispers of Madness work through a clear window? Will the Pipes of Haunting or a monster's Frightful Presence spread around a hallway corner? Can a monster ignore cover if the effect doesn't require sight?
Attacks and Spell Effects definitely require a line of effect between caster and target (See Cover Rules and Spell Targeting Rules), but I am unsure as to any RAW that would specifically deal with a line of effect requirement for non-spell, non-attack features.
The other typical rule is line of sight, which applies to any ability/spell/attack that requires you to see a target (or alternately for the target to see you). These are close, but functionally different things, since you can see a creature through a window but you don't have a clear line of effect to them.
As a DM, I would rule that in the absence of a clear overwriting rule, the non-spell, non-attack effect would specifically be subject to the limitations of its text, so the dragons Frightful Presence would affect all creatures who were within range and aware of the dragon, unless the dragon chose for them to be exempt (line of effect and line of sight don't matter). Portent requires line of sight but not line of effect, and the pipes require the ability to hear the tune in range but not a line of effect or sight. Don't have access to the Allip stats here but similar would apply (I would guess hearing from the ability title, but the text would rule)
DMs call really...I'd treat it like a standard spell AoE (line of effect enforced, total cover required to block it), but not subject to other spell rules (Antimagic Field wouldn't stop it)
Attacks and spells require line of effect to a target or point of origin. But what about other effects like class features, magic items, and monster actions? Will a divination wizard's Portent or an Allip's Whispers of Madness work through a clear window? Will the Pipes of Haunting or a monster's Frightful Presence spread around a hallway corner? Can a monster ignore cover if the effect doesn't require sight?
There's not really a section in the PHB or DMG that talks about abilities that aren't spells or attacks, it's kind of a conspicuous oversight. Also, there is no perfect sentence (that I'm aware of) in the DMG or Xanathar's which provides that "all features, magic items, and actions follow the same line of effect requirement as spells." However, there's one that is close:
The area of effect of a spell, monster ability, or other feature must be translated onto squares or hexes to determine which potential targets are in the area and which aren’t.
Not only spells, but monster abilities and "other features" are all lumped together and referenced to the same "areas of effect" rules. That's enough for me to show that the intent is that all effects should usually follow the example set by spell effects, and that that not only spells, but also all monster abilities and all "other features" use the same system presented in the PHB Chapter 10 for Areas of Effect, including point of origin/line of effect:
...Every area of effect has a point of origin, a location from which the spell's energy erupts. The rules for each shape specify how you position its point of origin. Typically, a point of origin is a point in space, but some spells have an area whose origin is a creature or an object.
A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total cover...
We also have the fact that in the MM Introduction, both Spells and Attacks of monsters are described as referencing the same systems as presented in the PHB, and not having any special exceptions to how they function on the battlefield:
A monster with the Spellcasting class feature has a spellcaster level and spell slots, which it uses to cast its spells of 1st level and higher (as explained in the Player’s Handbook)....
When a monster takes its action, it can choose from the options in the Actions section of its stat block or use one of the actions available to all creatures, such as the Dash or Hide action, as described in the Player’s Handbook...
Cover (and its permutations) describes in its introduction that it is relevent for "effects", but then dials in to "spell or attack" when describing Total Cover. I think that's poor editing, or indicative of the above oversight that led to nonmagical effects never being properly described anywhere:
Cover
Walls, trees, creatures, and other obstacles can provide cover during combat, making a target more difficult to harm. A target can benefit from cover only when an attack or other effect originates on the opposite side of the cover.
There are three degrees of cover. If a target is behind multiple sources of cover, only the most protective degree of cover applies; the degrees aren't added together. For example, if a target is behind a creature that gives half cover and a tree trunk that gives three-quarters cover, the target has three-quarters cover.
Half Cover
A target with half cover has a +2 bonus to AC and Dexterity saving throws. A target has half cover if an obstacle blocks at least half of its body. The obstacle might be a low wall, a large piece of furniture, a narrow tree trunk, or a creature, whether that creature is an enemy or a friend.
Three-Quarters Cover
A target with three-quarters cover has a +5 bonus to AC and Dexterity saving throws. A target has three-quarters cover if about three-quarters of it is covered by an obstacle. The obstacle might be a portcullis, an arrow slit, or a thick tree trunk.
Total Cover
A target with total cover can't be targeted directly by an attack or a spell, although some spells can reach such a target by including it in an area of effect. A target has total cover if it is completely concealed by an obstacle.
It's... thin, the sorts of in-game justifications for why the magic of a spell needs to be able to draw a straight line from its point of origin with no obstruction for line of effect aren't necessarily the same in-game justifications you'd use for something nonmagical like a scary noise, a bad odor, etc. But, in the absence of anything telling us how areas of effect and points of origin/line of effect work for nonmagical effects, I think that following the Spellcasting precedent identically is unlikely to lead to any truly absurd results.
I think I would agree with you Chicken, but mainly for effects described as actual AoE shapes (line, cone, sphere, cylinder, etc) or that could be "naturally" described as behaving similarly to an AoE shape. Outside of that, I do think the individual effect should weigh heavily on how far to take this as a "general" assumption. For example, you can feasibly hear pipes of haunting while being around a corner from where they are played, so should you be affected by its magic? I would think yes, as you have met all the requirements in the items description (range and hearing), and "naturally" sound would travel around the corner (barring an anechoic chamber of course)
Similar, a dragons frightful presence requires range and "awareness" but not sight. One can be aware of a dragon and inside a building, so if you meet the range and "awareness" rules, are you affected or not? "presence" doesn't necessarily behave "naturally" like an AoE sphere, even if the description describes a spherical effect centered on the dragon without using that actual term. Differently, its breath weapon is described as an actual AoE shape, so using the spell AoE rules makes "natural" sense.
The Balor's Death Throes are similar, but the way the explosion would "naturally" operate is very similar to an AoE sphere, so using the AoE rules would make sense even if the effect doesn't say "sphere"
Attacks and spells require line of effect to a target or point of origin. But what about other effects like class features, magic items, and monster actions? Will a divination wizard's Portent or an Allip's Whispers of Madness work through a clear window? Will the Pipes of Haunting or a monster's Frightful Presence spread around a hallway corner? Can a monster ignore cover if the effect doesn't require sight?
Attacks and Spell Effects definitely require a line of effect between caster and target (See Cover Rules and Spell Targeting Rules), but I am unsure as to any RAW that would specifically deal with a line of effect requirement for non-spell, non-attack features.
The other typical rule is line of sight, which applies to any ability/spell/attack that requires you to see a target (or alternately for the target to see you). These are close, but functionally different things, since you can see a creature through a window but you don't have a clear line of effect to them.
As a DM, I would rule that in the absence of a clear overwriting rule, the non-spell, non-attack effect would specifically be subject to the limitations of its text, so the dragons Frightful Presence would affect all creatures who were within range and aware of the dragon, unless the dragon chose for them to be exempt (line of effect and line of sight don't matter). Portent requires line of sight but not line of effect, and the pipes require the ability to hear the tune in range but not a line of effect or sight. Don't have access to the Allip stats here but similar would apply (I would guess hearing from the ability title, but the text would rule)
Edited for Spelling and Clarity
What about effects that specify nothing about sight, hearing, or awareness, such as the Balor's death throes?
DMs call really...I'd treat it like a standard spell AoE (line of effect enforced, total cover required to block it), but not subject to other spell rules (Antimagic Field wouldn't stop it)
There's not really a section in the PHB or DMG that talks about abilities that aren't spells or attacks, it's kind of a conspicuous oversight. Also, there is no perfect sentence (that I'm aware of) in the DMG or Xanathar's which provides that "all features, magic items, and actions follow the same line of effect requirement as spells." However, there's one that is close:
Within the DMG Chapter 8, we have this:
Not only spells, but monster abilities and "other features" are all lumped together and referenced to the same "areas of effect" rules. That's enough for me to show that the intent is that all effects should usually follow the example set by spell effects, and that that not only spells, but also all monster abilities and all "other features" use the same system presented in the PHB Chapter 10 for Areas of Effect, including point of origin/line of effect:
We also have the fact that in the MM Introduction, both Spells and Attacks of monsters are described as referencing the same systems as presented in the PHB, and not having any special exceptions to how they function on the battlefield:
Cover (and its permutations) describes in its introduction that it is relevent for "effects", but then dials in to "spell or attack" when describing Total Cover. I think that's poor editing, or indicative of the above oversight that led to nonmagical effects never being properly described anywhere:
It's... thin, the sorts of in-game justifications for why the magic of a spell needs to be able to draw a straight line from its point of origin with no obstruction for line of effect aren't necessarily the same in-game justifications you'd use for something nonmagical like a scary noise, a bad odor, etc. But, in the absence of anything telling us how areas of effect and points of origin/line of effect work for nonmagical effects, I think that following the Spellcasting precedent identically is unlikely to lead to any truly absurd results.
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I'm going to make this way harder than it needs to be.
I think I would agree with you Chicken, but mainly for effects described as actual AoE shapes (line, cone, sphere, cylinder, etc) or that could be "naturally" described as behaving similarly to an AoE shape. Outside of that, I do think the individual effect should weigh heavily on how far to take this as a "general" assumption. For example, you can feasibly hear pipes of haunting while being around a corner from where they are played, so should you be affected by its magic? I would think yes, as you have met all the requirements in the items description (range and hearing), and "naturally" sound would travel around the corner (barring an anechoic chamber of course)
Similar, a dragons frightful presence requires range and "awareness" but not sight. One can be aware of a dragon and inside a building, so if you meet the range and "awareness" rules, are you affected or not? "presence" doesn't necessarily behave "naturally" like an AoE sphere, even if the description describes a spherical effect centered on the dragon without using that actual term. Differently, its breath weapon is described as an actual AoE shape, so using the spell AoE rules makes "natural" sense.
The Balor's Death Throes are similar, but the way the explosion would "naturally" operate is very similar to an AoE sphere, so using the AoE rules would make sense even if the effect doesn't say "sphere"
The targeting rules can get confusing in some cases when effects only specify needing to see targets (since glass and divination are both a thing).
Ask the DM how they handle it.