The language in these rules indicates that total cover definitely works against attacks and spell effects (AOE or not), but what about effects that are neither attacks nor spells? Some game features, such as certain paladin auras, explicitly state that total cover stops them from working, but what about the game features that do not? If a class feature or monster ability only requires sight, does it work through windows? If it only states a range and has no other restrictions, does it flat out work through solid walls?
To target something, you must have a clear path to it, so it can't be behind total cover.
If you place an area of effect at a point that you can't see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.
Spells like fireball would also be affected by a glass barrier.
edit: note though, windows in 5e might commonly be simple openings that could be shuttered or covered at night or latices of small panes.
Cover affect spells, attacks and other effects that originates on the opposite side of it. Other Effect can include things like a Dragonborn's Breath Weapon for exemple or any effect the DM deem appropriate. Each effet should be determined if it only requires sight or if any physical obstacle can interfere with it.
Cover: A target can benefit from cover only when an attack or other effect originates on the opposite side of the cover.
The Dungeon Master Guide expand on Cover a bit more when discussing grid play.
Cover: To determine whether a target has cover against an attack or other effect on a grid, choose a corner of the attacker's space or the point of origin of an area of effect. Then trace imaginary lines from that corner to every corner of any one square the target occupies. If one or two of those lines are blocked by an obstacle (including another creature), the target has half cover. If three or four of those lines are blocked but the attack can still reach the target (such as when the target is behind an arrow slit), the target has three-quarters cover. On hexes, use the same procedure as a grid, drawing lines between the corners of the hexagons. The target has half cover if up to three lines are blocked by an obstacle, and three-quarters cover if four or more lines are blocked but the attack can still reach the target.
@puxah A group I'm in concluded that dragon breath goes through stone walls unimpeded because RAW total cover only blocks spells and attacks and breath is a non-spell save. I figure physics still apply, the breath would hit the wall, & folks inside are immune. Help? I figure the same should apply for paladin aura and other non-spell areas of effect. Hiding on one side of a 5' thick dungeon wall shouldn't affect the hallway on the other side.
@JeremyECrawford In D&D, everyday things—walls, gravity, bread, laughter—work the way we expect them to, except for when the rules say otherwise. For example, D&D has magical effects that pass through walls, for walls are assumed to be impenetrable, unless you damage the wall itself. #DnD
I don't want the dire troll to whirlwind someone through a solid wall, either. That seems like an overreach of what that monster can logically do, even though it's not an attack, spell, or AOE. My issue is that there is as much basis for claiming it requires line of effect as there is for claiming that Frightful Presence doesn't require line of effect: both kinda make sense. And I don't find that a satisfactory basis for rulings.
With Frightful Presence, you need to be within 120 feet of the dragon and be aware of it. Perhaps it's not as efficient when you're behind total cover when it tries to scare you.
A DM can always decide that effects that works upon being aware of something should not be impacted by physical obstable such as cover.
I don't want the dire troll to whirlwind someone through a solid wall, either. That seems like an overreach of what that monster can logically do, even though it's not an attack, spell, or AOE. My issue is that there is as much basis for claiming it requires line of effect as there is for claiming that Frightful Presence doesn't require line of effect: both kinda make sense. And I don't find that a satisfactory basis for rulings.
Additionally, what about effects that have nothing to do with real everyday things? If a monster can target a creature within 60 feet and deal psychic damage to it, we have no real world basis for determining whether line of effect is needed.
I don't want the dire troll to whirlwind someone through a solid wall, either. That seems like an overreach of what that monster can logically do, even though it's not an attack, spell, or AOE. My issue is that there is as much basis for claiming it requires line of effect as there is for claiming that Frightful Presence doesn't require line of effect: both kinda make sense. And I don't find that a satisfactory basis for rulings.
Additionally, what about effects that have nothing to do with real everyday things? If a monster can target a creature within 60 feet and deal psychic damage to it, we have no real world basis for determining whether line of effect is needed.
Usually the description of the effect will say if it can reach through solid objects, otherwise the default is for it to require line of effect.
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The rules for cover are found here:
https://www.dndbeyond.com/sources/basic-rules/combat#Cover
https://www.dndbeyond.com/sources/basic-rules/spellcasting#AreasofEffect
The language in these rules indicates that total cover definitely works against attacks and spell effects (AOE or not), but what about effects that are neither attacks nor spells? Some game features, such as certain paladin auras, explicitly state that total cover stops them from working, but what about the game features that do not? If a class feature or monster ability only requires sight, does it work through windows? If it only states a range and has no other restrictions, does it flat out work through solid walls?
Adding a bit more info on spells, the PHb also states:
A Clear Path to the Target
To target something, you must have a clear path to it, so it can't be behind total cover.
If you place an area of effect at a point that you can't see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.
Spells like fireball would also be affected by a glass barrier.
edit: note though, windows in 5e might commonly be simple openings that could be shuttered or covered at night or latices of small panes.
Cover affect spells, attacks and other effects that originates on the opposite side of it. Other Effect can include things like a Dragonborn's Breath Weapon for exemple or any effect the DM deem appropriate. Each effet should be determined if it only requires sight or if any physical obstacle can interfere with it.
The Dungeon Master Guide expand on Cover a bit more when discussing grid play.
Here's what the Dev had to say on this subject; https://www.sageadvice.eu/dragon-breath-goes-through-stone-walls-unimpeded-because-raw-total-cover-only-blocks-spells-and-attacks-and-breath-is-a-non-spell-save/
I don't want the dire troll to whirlwind someone through a solid wall, either. That seems like an overreach of what that monster can logically do, even though it's not an attack, spell, or AOE. My issue is that there is as much basis for claiming it requires line of effect as there is for claiming that Frightful Presence doesn't require line of effect: both kinda make sense. And I don't find that a satisfactory basis for rulings.
With Frightful Presence, you need to be within 120 feet of the dragon and be aware of it. Perhaps it's not as efficient when you're behind total cover when it tries to scare you.
A DM can always decide that effects that works upon being aware of something should not be impacted by physical obstable such as cover.
It seems more likely that you are behind total cover because you DID see a dragon :-)
Additionally, what about effects that have nothing to do with real everyday things? If a monster can target a creature within 60 feet and deal psychic damage to it, we have no real world basis for determining whether line of effect is needed.
Usually the description of the effect will say if it can reach through solid objects, otherwise the default is for it to require line of effect.