How would a DM and player balance a PC that would like to hinder themselves physically?

e.g. PC is blind or partially blind and would like to take a negative to perception

just brainstorming some options and would like some other thoughts

Completely up to DM. I personally am against it.

You might do something like 10 foot blindsight, blind beyond this distance.

I'm with DxJxC, things like this only make headaches for DM. I'm willing to work with things that are RP fluff rather than mechanical - like a magic Ersatz eye replacement for a lost eye or a magic prosthetic arm etc. Mechanically no difference but interesting in RP.

Take blindness for example: permanent Blinded condition is going to make the character a liability on a lot of things. Or we can go with the immensely overused and very unrealistic "blind master" trope - in which case it falls into the "no mechnical deficit, just RP fluffery" category and that's OK.

Maybe a critical role PTSD thing of a Wisdom save for a specific trigger or be stunned for a round. Something like that I can be OK with, depending on the trigger.

A friend of mine made a PC that was narcoleptic, and the DM had him roll every few minutes to see if it would kick in.  After the first session, the DM approached him and said while he appreciated the attempt to make a character with a real and serious flaw, it was also going to present a real problem for the game and he suggested my friend strongly reconsider that aspect of the character.  They ended up retconning it out for the next session.

I also really hate the amnesiac/Dory character trope. Just wanted that out there.

I've had more than one player (and I have only DMed for my group of 3 friends) be too lazy to make a backstory for their character, so the character defaulted to not knowing anything except their name and class features (but not how they learned their class features of course). Those characters are dead weight in RP, a hindrance even.

The only way I’d allow something like that is if that is how the player flavors a PC’s low ability score. For example, I’m near sighted and that’s a great way to flavor a low dexterity. But other than that I agree with not doing it. 

Thanks everyone. I didn’t really think about how much work it would be to keep track and make sure it was followed through with. 

for physical flaws i would stick mostly to rp stuff lost a single eye missing fingers ect. getting something  out of it  such as blind sight (really powerful ) doesnt really feel like a flaw now does it? im actually playing what is essentially what if an aberration could take on a humanoid form ( or i guess an old god tiefling). where i really play up the body horror random eyes/mouths tumors and tendrils ect. but none of it really provides anything aside from the fact that no one likes me T_T. 

or another idea i wana use is to play a war forged whose actually a paraplegic gnome piloting it like a mech. so sometimes i guess it really depends on how you can rebrand a race to fit what you need .

now dont forget the dangers of such flaws as well ok you have blind sight but you have no way of telling who was your ally and who wasn't; you just know there are 2 things standing right next to each other and they weren't in your range when they last moved. and you barb whose replaced his hands with swords is gana have a bad time climbing anything ect got to really thing about how dangerous or debilitating a flaw like that could be

Quote from Tim >>

The only way I’d allow something like that is if that is how the player flavors a PC’s low ability score. For example, I’m near sighted and that’s a great way to flavor a low dexterity. But other than that I agree with not doing it. 

 I really like this idea. I think that's the best way to handle something like this... at best I'd say to give the idea of a character with poor vision it would be fair to just give them a lower perception score than their Wisdom score would normally allow.