Lichen Stone Wall

The versions lining the underground jungle are background scenery and leave no item behind when you clear them. The only supply is the crafting bench, which is worth knowing before you spend an hour hammering at cave walls waiting for a drop that was never going to appear. What you craft is not quite the same thing either. Walls you place yourself count as safe and shut down enemy spawns in front of them, while the world's own copies do not, so a base carved into raw jungle wall stays noisy until you cover or replace every panel.

Spraying Dark Blue Solution across the area turns all four jungle wall types into Mushroom Walls, and the conversion ignores whether you placed them. Panels you hung by hand come out the other side unsafe. Grow a glowing mushroom biome over an old jungle house and you have quietly reopened the whole room to spawns without touching a single block.