Rules-as-written, you must be able to see the target of heat metal.
Heat metal says:
Choose a manufactured metal object, such as a metal weapon or a suit of heavy or medium metal armor, that you can see within range.
If you cannot see the metal object, you cannot cast heat metal on it.
A word to DMs: don't nerf your players' spell choices
Say you have a ...
Player's Handbook p.203
Once a spell is cast, its effects aren’t limited by its range, unless the spell’s description says otherwise.
From your example, Heat Metal says:
Until the spell ends, you can use a bonus action on each of your
subsequent turns to cause this damage again.
There is no range or LoS limit on this - they can run but they ...
If the Warlock is inside, NO. If they are outside, Maybe.
The real key here is the wording on Hunger of Hadar. The spell breaks itself down into being inside the sphere, and being on the outside looking in. We'll use that same breakdown as well.
A 20-foot-radius sphere of blackness and bitter cold appears, centered
on a point with range and ...
Jeremy Crawford has ruled No:
Devil's Sight is meant to pierce the dark created by a spell like darkness, not the void of hunger of Hadar.
As Crawford's tweets are no longer considered official rulings, and this question/answer does not appear in the Sage Advice compendium, I don't believe there is currently an official ruling on this ...
The rules assume that facing direction doesn't matter.
Therefore they routinely use "creature you can see" to mean "creature you could see, if you were to look in that direction". For example, opportunity attacks trigger when "a creature you can see" moves out of your reach.
If the spell was intended to operate only in the direction the caster is looking ...
Blindsight (monster ability)
A creature with blindsight can perceive its surroundings
without relying on sight, within a specific radius.
Creatures without eyes, such as oozes, and creatures
with echolocation or heightened senses, such as bats
and true dragons, have this sense.
This isn't super helpful mechanically, however it does mention '...
You do not need line of sight at all
Spells will tell you the requirements to cast them. All spells require (unless indicated otherwise), a clear path to the target, but line of sight is not a general requirement. In other words, spells only require line of sight if they specifically say so.
Here are the targeting requirements for wall of fire:
You create a ...
Rules as written: the subtleties of "can see" you're reading into don't exist. Whether you "can see" something mechanically means "you have line of sight to it." This heavily implied by the Player's Handbook, and finally made explicit in the Rules Compendium's section of Line of Sight on p106:
A few powers do require a user to be able to see a creature to ...
It is up to the DM.
Compare the description of other "Wall of ..." spells.
Wall of Fire's description says:
[...] The wall is opaque and lasts for the duration.
Wall of Force's description tells us that when you cast this spell
An invisible wall of force springs into existence at a point you choose within range. [...]
The Wall of Light
No. You don’t need to be within line of sight or within range to maintain concentration on a spell, unless a spell’s description or other game feature says otherwise.
The Sage Advice Rules of Spellcasting article on Wizards' site confirms this:
IF YOU’RE CONCENTRATING ON A SPELL, DO YOU NEED TO MAINTAIN LINE OF SIGHT WITH THE SPELL’S TARGET?
You don’t need ...
If your reading of a feature called See Invisibility is that you cannot see invisibility, your reading is incorrect.
It's quite simple, really. The intended function of these features is so abundantly clear, that any argument that concludes that they do nothing can be dismissed out of hand.
In fact, this principle applies in general. If you read a feature, ...
Yes, it is possible but...
The number of ways you can go about it is limited to somehow seeing through magical darkness like by getting Truesight.
Or by picking up 2 levels of Warlock for the Devil's Sight Eldritch Invocation, in order for you to see through magical darkness up to 120 feet.
Or by any means like the 6th-level Divination Spell True Seeing,...
You cannot cast the spell because spells require a clear path to their target
The counterspell spell requires us to see the target as it states:
1 reaction which you take when you see a creature within 60 feet of you casting a spell
And we can do this but the more general rule on spells from the "Targets" section states:
To target something, you must ...
This is obviously unintended.
Any workaround which utterly invalidates a mechanic is probably unintended and should be treated with extreme caution. You say it yourself:
if this is allowed, the proximity restriction completely disappears and you can curse whomever you feel like
You're proposing something which effectively removes a restriction from a ...
A character with devil's sight or even just darkvision, that is not blinded, can see into the area of the Hunger of Hadar.
According to the Sage Advice Compendium:
Magical darkness blocks darkvision only if the rules text for a particular instance of darkness says it does. For example, the darkness spell specifies that it produces a magical darkness that ...
Total cover blocks spells and attacks
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.
A target with total cover can't be targeted directly by and attack or a spell, although some spells can reach such a target by including ...
Range: Personal or targeted at yourself
Has a Target entry
You must be able to see or touch the target, and you must specifically choose that target.
When blind, your only solution is to touch the target. If you are the target, this is automatic. Otherwise, the Invisibility entry of the Glossary provides an option when the location of a ...
Things in D&D 5e do exactly what they say; no more no less:
When you are in dim light or darkness,
as a bonus action you can teleport up to 60 feet to an
unoccupied space you can see that is also in dim light
This does not grant you any ability to see into darkness, therefore, if you can't see into darkness you can't Shadow ...
Wanda is a valid target, only the effect is delayed
William has a clear path to Wanda, so they are a valid target for spells. Wanda is within sight so they are a valid target for Acid Splash.
Suppose William rolls an 11 and so:
the spell doesn't take effect until the creature's next turn
The next turn Wanda is out of sight and there is no clear path to ...
Here's the definition of Line of Effect:
is a straight, unblocked path that indicates what a spell can affect. A line of effect is canceled by a solid barrier. It's like line of sight for ranged weapons, except that it's not blocked by fog, darkness, and other factors that limit normal sight. A line of effect starts from any corner of your square and ...
Well, to start with, page 202 of the PHB, under Range, says:
The target of a spell must be within the spell’s range. For
a spell like magic missile, the target is a creature. For a
spell like fireball, the target is the point in space where
the ball of fire erupts.
So there's that. Then on the next page, under Targets, we have:
To target ...
The ability requires you to see an unoccupied space, but not through that space. You can teleport to any unoccupied space on the edge of the darkness spell effect because you can see the space of darkness (just not the through/past it).
For comparison, you don't have to see the entirety of a creature to target it with a spell that requires sight, just a ...
You do not need to be able to see the Mage Hand to be able to use it, otherwise ATs wouldn't be able to make the hand go invisible. However, working around corners (or otherwise out of sight) would effectively impart the blinded condition to any action you were going for. As such, you wouldn't be able to interact with a target except by guessing which ...
Line of Sight:
To precisely determine whether there is line of sight between two spaces, pick a corner of one space and trace an imaginary line from that corner to any part of another space. If at least one such line doesn't pass through or touch an object or effect that blocks vision - such as a stone wall, a thick curtain, or a dense cloud of fog - ...
Line of sight is irrelevant. Spells only require a line of effect unless otherwise stated.
As you quoted, the familiar can only deliver touch spells. Thus, the familiar must touch the target. So, in this particular case, line of effect is also irrelevant. If the creature can be touched there must be a line of effect via the contact.
If the spell calls ...
If source of fear is invisible, frightened creatures aren't affected by disadvantage.
A line of sight is the direct path between a viewer and viewable object [1,2,3]. Without an object to view, such as the cause of one's fear, there is no line of sight to that object. So when the a creature is not viewable, by hiding or invisibility, there is no line of ...
The target of heat metal must be visible
The spell states (emphasis mine):
[...] Choose a manufactured metal object, such as a metal weapon or a suit of heavy or medium metal armor, that you can see within range. [...]
Therefore, you must be able to actually see the metal you wish to cast this spell on when you cast the spell; however, the metal does not ...
The SAC gives a clear answer
Speaking of “line of sight,” the game uses the English meaning of the term, which has no special meaning in the rules.
And so, the meaning of "line of sight" is not a game-defined term and has no set meaning. It is natural English which means it requires context. The features you mention are obviously intended to work ...