Can Major Image and forced perspective make illusions appear larger?

In the game I’m running, the PCs are about to embark on a wilderness trek during which they will be harried by an opponent who has access to the major image spell. This opponent seeks to distract, mislead, and delay them, forcing them to spend more time and resources reaching their objective than they would otherwise.

I am trying to determine what is possible within the constraints of the major image spell description. One thing that occurred to me is that, while the spell’s effects are confined to a 20′ cube, they might seem to be spread over a much greater area by tricks of forced perspective. For example, an illusory, 20′ tall castle suspended in mid-air between the party and a distant hill might appear to be a full-size castle settled on the hill. Or a 20′ wide illusion of a wall of flames might seem to be consuming a vast span of the horizon.

Or alternatively, an illusory pit might seem to be much deeper than 20′ by "drawing" its walls and bottom in such a way as to make it seem deeper.

Can forced perspective be used with major image in this way?

Are there potential drawbacks to allowing this? Would any modifiers be appropriate for investigation checks to "disbelieve" them?

Do Illusionist’s Bracers actually allow you to cast two minor illusions?

The description of the Illusionist’s Bracers (GGR p. 178) states:

flavour:

A powerful illusionist of House Dimir originally developed these bracers, which enabled her to create multiple minor illusions at once. The bracers’ power, though, extends far beyond illusions.

effect:

While wearing the bracers, whenever you cast a cantrip, you can use a bonus action on the same turn to cast that cantrip a second time.

However to me it would seem that the effect provided would not actually allow one to cast multiple minor illusions at once because the description of the spell minor illusion states:

The illusion also ends if you dismiss it as an action or cast this spell again.

Am I missing something or does this magic item not actually allow one to do what its flavour text suggests?

How does Monster Slayer’s Hunter’s Sense work with illusions?

Would he receive information about the creature’s vulnerabilities based on what it appears to be, would he receive no information about the creature as if it were hidden from Divination magic or would he just understand that this is an illusion based on "magically" part of the ability description?

(…you gain the ability to peer at a creature and magically discern how best to hurt it…)

Creature telepathy and illusions?

I am running a D&D 5e campaign, and we had an interesting case come up in play last night.

The party cast minor illusion to conceal themselves in a cave at the end of a narrow canyon, and then a Spined Devil, with telepathy, spoke to them telepathically (and they replied).

Does the presence of the illusion mean that the Spined Devil could not have known telepathically that they were there?

In other words, since the party had been conversing while within the Spined Devil’s telepathic range, even though he was out of sight and ear shot, would there be any reason to think that he would not be able to ascertain their (general) location despite the illusion, once he arrived at that location?

Does the Observant feat allow you to auto-succeed against illusions?

The Observant feat states:

You have a +5 bonus to your passive Wisdom (Perception) and passive Intelligence (Investigation) scores.

To my knowledge, nowhere else in the rules is there discussion regarding a passive Intelligence (Investigation) score.

Furthermore, when added to a character in D&D Beyond, the Passive Intelligence (Investigation) is added under the character’s Senses akin to Darkvision or Blind Sight.

Several illusion spells include language along the lines of:

Can use its action to (do something to see through the illusion) and must succeed on an Intelligence (Investigation) check against your spell save DC.

Does the creation of a Passive Intelligence (Investigation) by the feat constitute a scenario of specific beats general rule whereby any illusion that can be defeated by an investigation check automatically fails if the save DC is lower than the passive score created by the feat?

Is breaking illusions like Phantasmal Force a kind of metagaming?

If I cast phantasmal force on an NPC to make him think a creature has jumped onto his back and is trying to strangle him, assuming he fails his initial roll, why would he use an investigate action?

Would it be that he suspects he is the target of an illusion? Would he know that investigating it would get rid of it?

Phantasmal Force also takes place during the player’s turn, so he still has his turn, but it seems like he would probably use his actual turn attempting to get rid of what’s attacking him, or if it’s say, a monster standing in front of him, he might attack it with his weapon. Would you count attacking or attempting to defeat it as an investigation roll, or does it specifically have to be that he is investigating it?

I can’t see many reasons why your average person would actually stop and study a monster. If it were an actual monster that jumped on his back, or an actual skeleton that was summoned to fight him, he wouldn’t investigate, he’d just try to attack. So I’m a bit confused about the investigation part, unless one of his friends shouts ‘the monster isn’t real, look closely’, but then they’d have to know he was fighting a monster and not just confused.

For the sake of roleplay, is it considered normal for anyone affected to simply make an investigation check each turn to attempt to end the illusion? Or is it considered normal for them to suffer during the player’s turn a monster on their back trying to strangle them, and on their own turn, perform some unrelated action like attacking a player with their sword while ignoring the effect?

How can I show the effects of illusions in Roll20?

My players are approaching a battle with Fraz-Urb’luu, who will have prepared the battlefield in some manner using an effect like Mirage Arcane and several other illusions and deceptions.

Given that I anticipate some characters having the benefit of True Seeing and others will not, is there a way for me to somehow present both the illusory and real battlefield? Ideally the method is practical to implement, but if I need to learn some technical skills to make this happen, that’s fine as well.

I typically will create my own maps using a combination of the blank background and whatever tokens I can find for free online. For example, my most recent map had the players fighting on Avernus, so I started with a red background, overlaid tokens on the Map layer to create mountains, sketched in linework and hatching for Styx and the portion of the Basalt Citadel that they could interact with.

The overall map was something like 60×75 squares. As we’re playing the game at very high levels, I’m intent on making large scale maps to allow players that have abilities that improve their mobility to enjoy that.

Can you cast spells through remote illusions?

The Project Image spell allows the caster to control an illusion of themselves from a significant distance away. They can see and hear through the eyes and ears of the illusion. The illusion can gesture and speak.

Can the caster cast spells (without material components) originating from the illusion? (through gesturing and speaking with the illusion)

Mislead has a similar effect, so the answer will likely apply to that as well.

Are there any other practical reasons for choosing proficiency in Intelligence saving throws, other than seeing through illusions?

Are there any other practical reasons for choosing proficiency in Intelligence saving throws, other than seeing through illusions?

It was suggested to me to take the Resilient feat. I considered taking Intelligence, but I can only think back to a handful of occasions where I used an Intelligence saving throws and it was always to do with illusion magic.

RESILIENT

Choose one ability score. You gain the following benefits:

  • Increase the chosen ability score by 1, to a maximum of 20.

  • You gain proficiency in saving throws using the chosen ability.

(PHB p. 168)

I mean, other than to have a better chance of seeing through an illusion spell, is there any point in having a proficiency with Intelligence saving throws?

It seems like it is the least useful out of all the saving throws proficiencies.

Dexterity, Wisdom and Constitution get used the most; Strength and Charisma less so, but Intelligence…

Of course, if you are in a campaign where illusions are very common, then yes I can see how this could be very beneficial, but for most campaigns I can’t see the point.

Are there any other uses for the Intelligence saving throw, such as to counter a monster’s special ability (other than an illusion)?

This is a question about saving throws, not ability checks.

Are lower level illusion spells capable of producing illusions that animate passively?

Can lower level illusion spells, specifically minor illusion, silent image and major image, create an illusion that can passively animate itself without requiring any further input on your part?

There have been a couple of other Q&As about this but they don’t seem conclusive.

  • Can Minor Illusion create animated illusion to Follow a creature? – I answered this, but wasn’t able to find anything that specifically suggested that minor illusion or silent image can be passively animated, so I assumed they can’t be.
  • Is Silent Image animated if an action is not used to move it? – the top answer suggests that silent image at least needs your action to be able to do, but there are comments arguing the lack of RAW support:

    The phrasing in major image is almost identical. It says nothing about the image moving “passively”. – Szega Jun 22 ’18 at 8:50

I’m guessing the answer will be definitely no for minor illusion, probably no for silent image, but I’m not sure about major image, and in all 3 cases, I wouldn’t know how to prove these assertions from their respective spell descriptions.