Dungeons and Dragons

Diversity for diversity's sake is not particularly effective at representation; do you have enough experience with down syndrome to write that character authentically and not from a place of stereotypes and slapdash research?

As a neurodivergent person and an Improv Teacher - there's a pretty good rule of: "when playing a [protected class] that you don't belong to play a specific person (whom you know) or don't at all" because otherwise that character is based entirely off stereotypes and is a bad choice

I think you’ve got some wonderful answers here already so I just want to add something that a few points brought to mind.

In my opinion one can authentically play a trait without playing a diagnosis. A great example of this is Drax in the MCU. He isn’t “the autistic one” he’s the guy with hyper literal interpretation. That autistic (amongst other classes) people relate that and feel seen isn’t because he’s “being autistic” but because he sees things like them; the other characters regard that and it somewhat authentically shows the outcomes one such person might have in these wild tales.

You can represent elements of neurodivergence without going all in on an ND character that might only serve to entrench stigma.

I think it’s an interesting idea, and that it could lead you and your party to explore some points of view that you might not otherwise get to really think about.

Your idea is making me think of the Asperger's community, as that’s the one I have the most familiarity with. Some mage class maybe.

If you want to do it right - that is, really use it as a learning experience - I would say read the bios of people like John von Neumann, Murray Gell-Mann, John Nash, and most especially Paul Erdos. These were some of the most brilliant mathematicians of our time (Murray was the guy who discovered quarks). George Price, too, although that one is pretty sad.

I am going to say that it’s going to make it a burden on your party members, and you should do it with their buy in, not make it part of the plot line that they discover it. If they’re not aware of it as a character trait and if you play it to the extent exhibited by some of those I mentioned, you’re just going to come off as an asshole. It’s really going to make things harder on everyone if you do it right. It’s a spectrum, so some in. The community can end up building self-awareness and develop coming mechanisms, but that wouldn’t be the point of playing that role.

Stereotypes are stereotypes for a reason. I have Aspergers which is a form of Autism, and I very much fit all stereotypes save for one. The key, much like real life, is focusing on the strengths so you can compensate for the weaknesses.

I don’t have experience with Down syndrome myself, but think about if you were in there shoes. If you knew that you learned things slower and communicated slower than your peers would you rely on those for day to day life? No, you would compensate in some other way. When people say blind people have super human hearing, they don’t. They’re just compensating for not having sight. When people say kids with Aspergers are super smart, I can personally attest that we are not. We just are compensating for our lack of people skills.

Any “disability” will be like this. You have a shortcoming that no one else has to deal with, so you compensate somewhere else. If you want people with “disabilities” to shine in your story, focus on their strengths and have characters around them who can prop them up in their weaknesses. That’s definitely a conversation you need to have with your table, because if there’s no one, or no way to compensate for a weakness it’s like trying to build a house with sticks and stones. You’re basically going to end up with a hole in the ground, functional, but royally sucks. The surrounding people are extremely important to a neurodivergent’s success as that is what gives them the tools to build with, and if you have tools you can build a proper house.

I find it fun to play my characters with various symptoms of my own neurodivergence. And the occasional NPC in a game I'm DMing will stand out this way as well. I find it adds variety and makes things more real and interesting. A great way I found to include neurodivergence that can have game mechanics tied to it is Limitless Heroics by Wyrmworks, so you could check that out.

Well one don't worry about offending people that aren't the table. Its not a performance that the world will see. Second as the gm you just tel the player what the npc does, what they say, etc etc. So displaying a nps that has any conditions comes down to observable behavior quirks.