D&D 5E Effective Illusions

[jaelis]

RAW are null on the point, but from my view, illusions must generate light t be seen as there is no surface there for light to bounce off. The light reaching our eyes must come fom somewhere. Of course it must be magical light as it creates different optical results for different people (based on if they have successfully investigated it or not).

They don't need to generate light if they are all in the observer's head.

 

[Seramus]

One of the best uses is just making duplicate party members. It's like a poor mans Mirror Image.
You make the appearance of multiple people step out and move around a party member in a confusing manner, and now the monster has to pick which one of them to attack. They are all slightly overlapping, so they are all in contact with each other, so it's one continuous image. But you can basically make 8 replicas of the same person in a single 15x15 cube ( or more if they are flying ).

Only downside. Since it's technically just one illusion, seeing past one means seeing past them all.
But then Mr Warlock just casts it again next round.

 

[Eltab]

Oddball illusions:
- The hallway continues thataway beyond the range of your light. Do something to scare the enemy into fleeing thataway. First guy crashes into the real wall and a traffic jam ensues. Now cast Fireball on the conveniently concentrated mob of foes.
- The hallway does NOT extend any farther; you see a dead end. The PCs all stand quietly down the hallway behind the fake wall and let the enemy go by.
- A bunch of kids pass by. Useful when both sides wish to not be discovered or made public.
- Romeo and Juliet are playing kissyface in an alcove (or are hot-and-heavy necking in a closet, if you have a 'sound-only' version). Whose reputation did you want to besmirch?
- Very drunken Lord Huffandpuff staggers across the ballroom.
- Illusory copy of somebody who has bragged that he can hold his liquor, getting sick to his stomach over the ship's railing.
- Create an illusory person. Publicly challenge it to a duel, to show how good you are with a blade.
- Several stumps / bushes / &c are an area of difficult terrain.
- Zone of sticker weeds (thorny). Make the Druid jealous he didn't think of it first.
- Illusion of a tall hedge, with the Rogue/Assassin hiding within fully prepped for an Alpha Strike sneak attack.
- Cast the illusion over yourself to look like somebody harmless (like a toddler)
- "Look - over there! A Mind Flayer! Everybody RUN!" Or have it sneak up behind you in plain sight of the enemy.
- Subtly alter your group's appearance so you look like you are "normal people" wearing Halloween costumes.
- Combine with Tiefling's Thaumaturgy so he not only makes a grand entrance into the room, everybody thinks they are looking at Darth Vader (or similarly impressive personality).
- A bunch of the enemy horde just failed their morale roll and run away, in plain view of the rest of the horde. Variant: they run off to the side of the battlefield and you yell "Oh no - they're gonna plunder the wagon train!"

 

[Irda Ranger]

I'm playing a GOO Warlock right now and I'm using my Minor Illusion and Misty Visions for all sorts of things.

I've hidden the entire party behind a fake wall (just standing 1' in front of the normal wall) several times.

We were sent to acquire a magical beast. We didn't but I made an illusion of us having it with us on a leash, so they let us back into their camp anyway.

I hid inside an illusionary wine barrel.

I made an illusion of the party standing 30' away to waste enemy attacks and get them to reveal their position.

We disguised ourselves as mercenaries and I added a couple orcs and an ogre to our party to sell that weren't the good guys.

I moved a small footbridge 10' to the left. That was a good one.

We ran away and turned left at a T-intersection and dived into an alcove. I made the sound of us running away to the right.

 

[Irda Ranger]

RAW are null on the point, but from my view, illusions must generate light t be seen as there is no surface there for light to bounce off. The light reaching our eyes must come fom somewhere. Of course it must be magical light as it creates different optical results for different people (based on if they have successfully investigated it or not).

I take the exact opposite view. The illusion is a magical surface that reflects light but does not generate any. Yes, this allows mirrors, but it disallows illumination.

Making your save means seeing through the fake surface.

 

[Satyrn]

I have a player that used phatasmal force to create a locked metal box surrounding a foe's head. They get saves but otherwise they are blind and in fear of suffocating. I allowed it on the fly, but am not sure about if this becomes a regular tactic.

And this leads nicely into what I'd advise. Make it clear to your DM that you won't spam one or two tactics over and over. This way he ought to be less inclined to nerf your illusions for fear of you "getting one over on him" with your creativity.

 

[jaelis]

I take the exact opposite view. The illusion is a magical surface that reflects light but does not generate any. Yes, this allows mirrors, but it disallows illumination.

So you would say that you can't create an illusory light source, like a flame? That seems more limited than what a spell like major image describes.

 

[Sir Brennen]

That makes a fair amount of sense. Many thanks for the clarification. What about light selectivity in an
illusion? Can an illusion be used as a customized light source? I was thinking about light sources that can only be seen by people with
infravision or ultravision. Or adjustable light sources for non combat environments. What would your take be?

Fortunately, infravision and ultravision are not a thing in 5E, so for this edition, that question is moot.

But as has been pointed out, to be perceived, an illusion must either be emitting (or reflecting) light, or being implanted directly into the brain of the perceiver.

Per the SRD's description of illusion magic:

Illusion spells deceive the senses or minds of others. They cause people to see things that are not there, to miss things that are there, to hear phantom noises, or to remember things that never happened. Some illusions create phantom images that any creature can see, but the most insidious illusions plant an image directly in the mind of a creature.

So, there is a RAW distinction between illusions that exist only in the mind and those that are outside it. The former applies to spells like Phantasmal Killer, while the latter to Minor Illusion and Major Image. I could see the argument for Invisibility going either way.

Minor Illusion's description says it can't create light (i.e, you can't create an illusion of a torch with it), so I'd say illusions are created by manipulating the way light is reflected back to a person perceiving it - the light bouncing off a wall is changed to look like it's coming off of something else in front of it. Minor Illusion doesn't have the juice to "boost" the light to be an actual light source.

But regarding the strength of the light of something from a more powerful spell like Major Image, which has no restrictions on creating light: could you have a Major Image of a bull's eye lantern, and shine it's light to illuminate an object 60 feet away? Sure, why not ... if that's what you want to blow a third level slot on. As long as the source is in the spell's AoE, the light it casts can exceed the AoE. Even then, I might put limits - the light output can't exceed a large bonfire, for instance. And seeing through an illusionary light source would dim it by half for that creature.

 

[Andrew Blair]

Illusions being more a matter of psychology than optics. An illusion of a magniying glass wouldn't start a fire with sunlight. An illusory telescope would not bend the incoming light to create an enlarged image.

 

[Andrew Blair]

Final clarification then. Can an illusion block light? Using the Phantasmal Force example from before actually interrupt the Medusa gaze? Or does the illusion make you think you are looking at a box, giving your statue an unusually calm expression? If it can block light and can stop the gaze attack, would a minor illusion of a towel be enough?