I got this inspiration from a twist the wish post, so here's like a homebrew material plane world called Moonwinter. Moonwinter is the remains of an earlier world that one day, the sun set and never rose again. The final sunset was cause of the god Svinterkril (god of Moonwinter-NE -Moon made of falling snowflakes) pushed the sun down and held it in prison. Moonlight is the only source of light which is very dim (anyone born in Moonwinter gains darkvision for 60ft). Crops cannot grow, many people die of the magic cold, and so on. So one person (gender, race, and name unknown) known simply as The Supreme Radiant One attempted something a normal person would find insane, they burned themself alive. Miraculously, they were reincarnated, shining and warm, and then they caused themselves to burn, they went outside to the farm, and the crops grew! They taught others this creed, meant for people to burn, reincarnate, and follow the path of light. This introduces a new class called Radiant One. Radiant Ones are devoted to healing of the magic cold and killing the monsters of Moonwinter. To protect themselves from the cold, villages have lamp-lighters, people who light lamps to protect from the cold, this adds a new background called The Lamplighter.

I would really appreciate feedback so thanks!

Sounds like dark souls.

Never played that but ok.

I think there are a lot of questions unanswered. The biggest right now are:

Since crops died, how do any plants survive?

How do any animal, not just people, survive without plants?

And what the hell are the rest of the gods doing during all this?

That's were i think all of y'all come in, to help decide. For the second one, well my brother (EEDNB) said that herbivores learn to photosynthesize and they also eat Moonberies which get there energy from the moon, not the sun. The crops grow quickly at harvest, where the lamp-lighters and Radiant Ones bring light to the farms and the crops grow. So peoples main diet is meat. The gods idk i need help with that.

About the photosynthesis, I was thinking rather than learning to photosynthesize, the animals evolved to photosynthesize through mutations and whatnot. About moonberries, I was thinking they still photosynthesize, but they are sensitive enough to survive with just the moon. Same with the animals. As for the gods, maybe before the sun shenanigans, Svinterkril massacred them all (lets assume they can die but will come back) and then caused Moonwinter to happen. Afterwards, Svinterkril banished them away from Moonwinter, and they couldn't break it as Svinterkril was in fact the creator of the world, and had planned for this all along.

You have an opportunity to develop some method for how plants, and by extension animals, survived after the sun was captured.

Evolution is a long process, too long to explain new abilities. I suggest coming up with alternatives.

I like the idea of using the moon, maybe presenting it as a personality onto itself, trying to help.

How about moonstone, which amplify the moonlight to help plants? They would become more valuable than gold, especially if some were better than others.

Or maybe evolution occured when the gods acted to protect the earch, changing plants to suit the now near lightless eternal night. 

I think if you can come up with an interesting way to answer this, your world will be amazing! And we haven't even talk about undead or the underdark!