Can you safely assume that Beholder's rays are visible and audible? (based on rules / lore / novels / famous campaign streams, etc)

Question

Some context: We're running Dragon Heist and the party is facing Xanathar himself. This question actually was caused by this discussion about the tactics of a party trying to distract the Beholder and use that moment to execute an epic party combo against him. Basically, the plan is to force the Beholder to waste his alpha-strike on an illusion and then, right at the moment when the party SEES or HEARS that Beholder has just wasted his deadly shot, the party would fire with everything they've got.

But then one of the community members with close to 200k reputation told me this:

You have assumed that the eye rays are perceptible - the rules on beholders don't actually say this.

This comment puzzled me... Indeed, if that's the case and the rays are not perceptible, then the party simply can't hear or see the attack, then the whole "strike all at once when he shoots with his rays" plan won't quite work...

Indeed, there is nothing in the rules saying that the Beholder's rays are perceptible. But should it be based solely on the rules? There may be no text in the rules saying that a fireball would create a hole in an ice sheet and creatures could fall in it, forced to do Athletics and CON checks, but that's exactly what happened in our campaign in one of the boss fights and it was awesome!.

Like with the "fireball cracking the ice" example, I assume that it's my job as the DM to have the world meet my players' expectations. These expectations should probably be based on some D&D novels, Sage Advice clarifications or "famous DM precedents". But as a newbie DM I haven't read lots of that. Maybe I'd have a player who have seen a Critical Role stream where Matt Mercer creatively describes how the Beholder's rays interact without any sound and visible effect... Or the opposite...

All that I did was check a basic google images search and it sorta shows that the beams are visible:

So, is there any good lore / novels / famous campaign stream examples of fights with a Beholder that could shed some light on how his rays should actually work in the D&D world? Is it safe to assume that the rays are visible and audible? I really want to be prepared for my party, because this guy Xanathar is pretty important for the campaign and I want to roleplay him right and not give a bad ruling on the way his rays work.

Answer 1

We have confirmation about the rays being visible from Elminster's adventures.

In the novel Elminster - The making of a mage by Ed Greenwood, the very creator of the Forgotten Realms, we have the description of a battle between Elminster, a dragon and a beholder.

In this part of the book, Elminster is transformed into Elmara, a Human female and a cleric of Mystra, in order to make El learn the deepest connection with the Weave, a connection that only women can feel.

El, together with a party of adventurers, is trying to rescue a book guarded by several monsters: one of them is a beholder, a death tyrant. In some passages, it is clear that the magical rays are visible, by the verbs employed to describe the battle (emphases mine):

El saw more than one eye spurt gore or milky liquid and go dark before the madly spinning eye tyrant blasted the shards into drifting smoke with a ray that leapt on to stab at a certain young mage.

[...]

Stabbing rays of radiance leapt from the beholder's many eyes.

[...]

The monster [the beholder] squalled in pain and fury as it tumbled to a halt. What eyes it had left turned toward the nearby balcony.

Bright beams and flickering rays of feebler radiance flashed, and the Blades [El's party] cried out and ran vainly about the balcony in terror. It shook and shuddered under them, and most of the rail was suddenly gone, melted away in the fury of the eye tyrant's attack.

[...]

The blackened eye tyrant rolled over in the streaming storm of flame so all its remaining eyestalks pointed straight at the great wyrm. Rays of magic leapt and thrust, and the oncoming dragon began to scream.

[...]

Rays and beams flashed out again. Through that bright fury, the Blades saw Elmara raise one arm as if to lash the beholder with an invisible whip.

The above descriptions denotes that the rays and the beams coming out from the eyestalks of the beholder are visible.

Answer 2

Does it matter if there is lore and rules?

Your question is contradicting.

I really want to be prepared for my party, 'cause this guy Xanathar is pretty important for the campaign and I want to roleplay him right and don't give a bad ruling on the way his rays work.

versus

Indeed, there is nothing in the rules saying that the Beholder's rays are perceptible. But should it be based solely on the rules?

You are asking if there is a rule, but don't want to base it on rules.

There are no secret rules in D&D 5e. The stat block for beholders does not mention that there are visible or audible indicators when the beholder uses a ray, so there doesn't NEED to be an indicator.

This is your world

You are the DM. In the opening of the Dungeon Master Guide

This book, the Player’s Handbook, and the Monster Manual present the default assumptions for how the worlds of D&D work. Among the established settings of D&D, the Forgotten Realms, Greyhawk, Dragonlance, and Mystara don’t stray very far from those assumptions. Settings such as Dark Sun, Eberron, Ravenloft, Spelljammer, and Planescape venture further away from that baseline. As you create your own world, it’s up to you to decide where on the spectrum you want your world to fall.

The listing of monsters in the Monster Manual (and any other rule book you incorporate) are guidelines. If you think it's cool that beholders beams make pew pew noises and/or have a colored beam for each of the rays, then let it be! Use the Rule of Cool as needed.

Make the narrative work how you think it should work

If you think it will improve the story to have visible beams, do it. If you think it would by funny that the party will need to scramble because they didn't research the fact that beholder beams are unnoticeable, play it that way. Maybe Xanathar is different than normal beholders and his are invisible instead of all the other beholders being visible? Maybe in his hubris he announces his attacks similar to a manga character?

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Side note: The reason art has beams is because without it, the beholder would just be having a staring contest. It's there to add context to what's going on, it doesn't imply that beams have colors. Also along the lines of manga, the characters announce their attacks so the reader knows what's going on. The "Planet slicer" ray looks identical to the "Cook lasagna" ray on the printed page.

Answer 3

The rules don't say, it's up to you

The text of the beholder just says:

The beholder shoots three of the following magical eye rays at random

neither this nor the description of any of the rays states if the rays are visible or not.

Image Evidence

Yes, numerous images show Beholders shooting visible eye rays, and many of them are published by WotC. However, this is not conclusive evidence:

• It is natural for an artist to use visible rays to show what is going on, as it makes for a much better picture. Imagine showing the beholder without the rays (as they are invisible) -- that would be way less cool and visual.
• Much of this material is from Magic: the Gathering. While I think the teams talk to each other, and probably have members that play both games, MtG is not an official source as far as the D&D rules are considered. The beholder picture in the MM does not show any rays.
• There is also pretty strong counterevidence, from the very cover of the Monster Manual: this shows a beholder in full battle mode against some characters, and there are no visible rays to be seen anywhere:

Spell Evidence

There is another source of suggestive evidence: the spells that those rays emulate. Especially the disintegration one. The disintegrate spell says:

A thin green ray springs from your pointing finger

And the enervation ray has a matching enervation spell that states:

A tendril of inky darkness reaches out from you

So, maybe some rays are visible, and some are invisible. Sleep, Charm etc. do not have any such language.

Precedent

Matt Mercer and Critical Role are great, but they are not an official source of material, rules or rulings for D&D in general (except for the material published on their game world by Wizards). So, while you can get inspired by their (or others) precedent, if this should or should not influence you is up to you.

However, the beholder also does not say the rays are invisible. With no guidance from the printed rules, you can turn to Tasha's Cauldron of Everything, page 4 (my favorite piece of rules text):

The rules of D&D cover many of the twists and turns that come up in play, but the possibilities are so vast that the rules can't cover everything. When you encounter something that the rules don't cover or if you're unsure how to interpret a rule, the DM decides how to proceed, aiming for a course that brings the most enjoyment to your whole group.

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P.S. I agree with your ruling on the fireball melting ice, but strictly by the rules this would not happen. Ice is not a flammable object, and all fireball does to non-creatures by its text is to ignite flammable objects.