Darksight - Inverting light and dark to see in darkness and be blinded by light

[Greywander]

Basically, a creature who sees shadows instead of light. They see in darkness as if it were bright light, and in bright light as if it were darkness, inverting how light and darkness affects their vision. You get shades of this with Sunlight Sensitivity, but that's still primarily light-based vision.

[Segev]

It could be interesting. Of note is that this would give such creatures the best darkvision imaginable, letting them see out to any distance (at least as far as normal-sighted creatures can see in daylight on the surface) in the dark. Dwarfing even the range of the Twilight Cleric's darkvision, and at least matching the efficacy of a drow barbarian with the eagle totem at 6th level (who can see out to a mile with darkvision, thanks to a quirky rules interaction).

[Greywander]

The trade off being that a humble torch can conceal the party. There's a reason Light is a cantrip and Darkness is a 2nd level spell.

This is also why I don't think this would be a good trait on a PC. While a monster can just live in a dark cave forever, the PCs will often find themselves in bright light as they travel around. It's about 100 times worse than sunlight sensitivity, since even indoor lighting will blind them. And as long as there's at least one party member without darkvision, you'll need to bring a light along for them anyway.

Sidenote: I remember asking about the eagle barbarian and things like darkvision, and the way it's worded doesn't extend things like darkvision. It allows you to see out to 1 mile, and to perceive fine details as if you were only 100 feet away. That's not the same as saying that your vision out to 1 mile is as good as your vision out to 100 feet.

[Segev]

The trade off being that a humble torch can conceal the party. There's a reason Light is a cantrip and Darkness is a 2nd level spell.

This is also why I don't think this would be a good trait on a PC. While a monster can just live in a dark cave forever, the PCs will often find themselves in bright light as they travel around. It's about 100 times worse than sunlight sensitivity, since even indoor lighting will blind them. And as long as there's at least one party member without darkvision, you'll need to bring a light along for them anyway.

Sidenote: I remember asking about the eagle barbarian and things like darkvision, and the way it's worded doesn't extend things like darkvision. It allows you to see out to 1 mile, and to perceive fine details as if you were only 100 feet away. That's not the same as saying that your vision out to 1 mile is as good as your vision out to 100 feet.

I could argue about the barbarian, but I feel that's off topic, and it's one of those things that a DM would only allow if he was okay with the stunt anyway.

Agreed on all the problems it would cause. I said it could be interesting, not that it was necessarily a good idea. I figure if you're implementing it, you'll need to design the story around it, or create mechanics to support it.

[Psyren]

This could make for an interesting "puzzle monster."

It wouldn't be appropriate for PCs.

[Greywander]

Yeah, I do think it would be interesting for a monster. I like the idea of a puzzle monster. It would be kind of tricky to implement, and might not fit D&D's design philosophy. You could, for example, have a very strong monster, so in darkness you'd risk a TPK. But all you'd need is a simple torch to, well, maybe not trivialize, but to certainly make the fight a lot easier. The problem is that there isn't really an in between: it's either a deadly fight or an easy one. And it's not like light is hard to come by, so the "puzzle" would need to rely almost entirely on figuring out the monster's weakness, rather than procuring the thing they're weak against.

Mostly I was curious why we didn't see anything like this in the game, but after thinking through it I think I can understand why. It's trivially easy to overcome such a weakness, and it would be hard to balance a monster for both exploiting and not exploiting the weakness. Still, I think this is something that could be implemented.

One possibility would be to use a monster such as this as an incentive in certain areas to bring a light, even if the whole party has darkvision. TBH, needing to maintain a light source at all times would add some tenseness to the atmosphere, and you could throw in various things that try to snuff the light out, or split up the party to separate the person with the Light cantrip from the others.

You could also use this to make the world more interesting. If you have a civilized race of creatures with darksight, then they might have things like dark torches that create areas of darkness. Such items would probably be pretty valuable for adventurers. If such a society was very open to outsiders, they might also have light sources that create dim light (in fact, it could either cast dim light in darkness or reduce bright light to dim, which is also interesting), which is less than ideal but would allow both the outsiders and those with darksight to at least somewhat see.