No matter how many hours you've put into Elden Ring, there's just no way you can predict what nightmarish creature or terrifying place you'll find around the next corner. So when players came across an illusory wall that took 50 hits to disappear, they just went along with it because it sounded like something FromSoftware would do. It was only later that we found out that it was indeed a bug all along, which finally got patched.
Players have now found a random wall that inflicts poison build-up upon contact, and no one was sure whether it was a bug or a trick by the developers. Thankfully, FromSoftware aficionado, Zullie the Witch took it upon themselves to investigate this wall and deduce where it got its toxic traits from. In their video, Zullie explained the process via which the wall may have received the ability to perform poison buildup, and how the mechanic works (thanks GameRant).
"It's caused by a feature called Hit Material," they explained. "Hit Material is used to define the terrain so the game knows, for instance, if what you're walking on is stone or dirt. This tells the game what audio, like footsteps, it should use, but it's also used to set things like lava dealing fire damage. This samke system is what makes poison swamps poisonous, by assigning a special effect to the floor you're walking on."
Zullie then went on to explain that poison effect is inflicted as long as the player is in contact with a surface with poison Hit Material. They also elaborated on a feature called 'wetness' via which the character is painted in the effect and takes continuous build-up damage, even when not in contact with the surface. So, to sum it up, the developers mistakenly gave the wall a Hit Material, leading to the poison build-up.
"The only error is just that the wall was given Hit Material 25, the same as the green muck, so it should be a simple fix," concluded Zullie. So it turns out that this was a bug as well, and perhaps FromSoftware devs aren't as devious as we make them out to be.