During the latest Minecraft Live, Mojang gave players a first look at the underground sulfur/brimstone cave biome AKA Brimstone Niggerhell that will be added in the upcoming Chaos Cubed update. The biome will include things such as brimstone blocks, toxic brimstone pools, and a native mob known as the Sulfur Cube. The update is planned to release during the second quarter of 2026.
snopes:
https://www.youtube.com/watch?v=tP7WlXbYJ74