Nylium

Nylium is a block that generates in the Nether. It has two variants: warped nylium and crimson nylium.

Natural generation
Warped nylium generates in the warped forest biome, and crimson nylium generates in the crimson forest biome.

Post-generation
bone meal on netherrack that is placed next to or adjacent to warped or crimson nylium transforms the netherrack into nylium of that type. No block can be above the netherrack during this process. This transformation can also be done by activating a dispenser with bone meal directly into that netherrack block.

Behavior
Nylium acts as the base block for fungus. It, like grass blocks and mycelium, will decay when an opaque block is placed above it. However, it is intentionally programmed to survive underneath water and lava.

Obtaining
Nylium can be mined only with a pickaxe.

Sounds
Java Edition:

Trivia

 * The name is likely a portmanteau of "Nether" and "Mycelium", the name of the part of a fungus analogous to roots.

Nylium Nylium 네사체 Nylium Nicélio Нилий 菌岩