Are there any monsters that are deaf? Would it show up on stats blocks?

Question

First time DM here.

I had an issue in a session recently, where my party fought a Gelatinous Cube, and the Bard decided that this monster must for sure be unable to hear, so it wouldn't make sense to use Vicious Mockery. I told her, that there is nothing on the stats block that says it was deaf. It only says it has blindsight, but nothing about it's hearing. She was annoyed. I guess she saw it as meaning that she can't apply common sense on deducing monster stats/resistances/etc, which I understand can be frustrating.

I was a bit of a wise-ass and pointed out that a gelatinous cube might be able to sense vibration in the air in its entire body and therefore be actually very good at hearing, but that didn't really make things better...

My question is now: Was it right for me to assume that if the stats sheet says nothing about its hearing, I can assume the monster has hearing? Or would it have been my responsibility to rule whether this monster can hear? Are there monsters that don't have hearing? What would it say on the stats sheet?

Thanks!

Answer 1

Note that a gelatinous cube has "Condition Immunities: Deafened", which either suggests that it can hear, or (possibly) suggests that it cannot hear and therefore cannot be deafened.

One of the design principles of 5e is to not include every rule, and to expect the DM to fill in the details. One example of this that comes to mind is this old question about what happens if a druid wears armor. (The rules just don't tell you, so you have to make something up!) The question of whether monsters have hearing seems similar.

Here are some principles that I follow as a DM, which might be helpful to you:

• Always try to interpret rules in a way that lets characters use their abilities. Players have more fun if their characters can use their abilities; players have less fun if their characters are useless. If someone asks you "hey, can that gelatinous cube hear my vicious mockery?", this suggests that you should answer yes, to allow their character to be useful.
• Try to work with the players' worldbuilding if you can. Players have more fun when you say "yes, and"; they have less fun when you contradict them and say "no, that doesn't work". If your player decides that the gelatinous cube is obviously deaf, or if they decide that goblins are terrified of horses, or if they decide that there's a Thieves' Guild in this town that they can talk to: go along with it, make it part of the story.
• If a character believes something is true, you as DM can't reach into their mind and contradict their belief. If the bard believes Vicious Mockery won't work, then maybe that's true and maybe it's false, but consider letting them believe that. (Especially if they're going to do something creative to work around the "problem".)

I've found that players are happier when I follow the above.

In the case you describe, I would have secretly decided that vicious mockery can work on a gelatinous cube because of magic, but I would've let the bard continue to believe that it wouldn't work as long as they had something different they wanted to try.

If the bard started to feel like none of their abilities was any good, and it looked like they were feeling useless and frustrated, I might offer a hint: "You seem to recall that the magic in your vicious mockery is pretty flexible, and it works on a lot of things. You're not sure if it'll work here, but it might be worth trying just to see..."

Answer 2

A Skeletal Swarm is always deafened unless it somehow gains immunity to deafened.

The Skeletal Swarm from Ghosts of Saltmarsh has a feature called Deafening Clatter:

Creatures are deafened while in the swarm’s space.

Since the swarm is in the swarm's space, and is not immune to deafened, it is technically always deafened unless it somehow gains immunity to deafened.

Beyond this, I am unable to find any creature that is stated to be inherently deaf.

I have always assumed a creature could hear unless it was subject to the deafened condition.

Now that you describe it, I can definitely see the problem here. After reviewing the PHB, DMG, and MM, hearing seems to be totally unaddressed outside the Deafened condition. So the next best thing I can offer is the way I have always ruled it: I have always assumed a creature could hear unless it was subjected to the deafened condition. I think the biggest advantage to this is a reduction in DM overhead for having to keep track of monsters that you have decided are inherently deaf.