There are two endings in Dark Souls. It's not clear whether one is good or bad — they're just endings. Or maybe not! According to a player who'd dug around in the code, From Software actually knows which ending is the "good" one."
Warning: There are spoilers for Dark Souls ahead, obviously!
An unused value called ClearState was discovered by IllusoryWall, who constantly tests the Souls games for "cut content or other oddities."
ClearState suggests three options: none (0), good (1), bad (2). This is changed when the player picks an ending in Dark Souls, and begins their New Game Plus adventure. In the screen shot above, the player chose the "good" ending for the game.
"I don't believe this provides any useful insight to the lore," wrote IllusoryWall, "but it at least tells us how the developers were referring to the different endings."
As a reminder, here's how the endings for Dark Souls work out. When you defeat the last boss, Gywn, you have two options. (If you're like me, you might not have even realised there were two endings, since the game doesn't make both options explicit.)
One, players can light the last bonfire. Dark Souls takes place in a bleak, decaying age that's been perpetuated by feeding the fire. By lighting it, you're agreeing to continue the status quo, essentially taking the place of the very person you defeated. Ultimately, your soul will crumble, as well, and another person will have to make the same decision as you. Recycle or reborn?
This is what the game considers the "good" ending.
The other ending involves the player breaking this cycle and unlinking the bonfires, becoming the new Dark Lord. Unfortunately, you're also bringing the current age to an end, which means you don't have very much to rule over. That said, it's an opportunity for the world to move on, allowing a new age, the Age of Darkness, to take over. Age of Darkness? Sounds thrilling!
This is what the game considers the "bad" ending."
IllusoryWall double checked, and these don't have anything to do with triggering achievements, but it's very possible From Software never intended the game to be interpreted this way. It's possibly discarded code, as the Souls game are famous for having lots of cut content and features that linger behind the scenes.
In the reddit thread discussing the discovery, people had some theories leaning in this direction.
If nothing else, it's amazing there are still things to discover about these games, years later.