Fog World Mod 1.8.1, 1.12.2 adds configurable cloud to the Minecraft world. This mod is for modpack developers or players who wish to control Minecraft fog. You can adjust the fog density (thickness), and color using the configuration options. You can also blacklist specific dimensions and biomes from fog spawning.
Fog World has the ability to make the fog poisonous upon direct contact. This is not available by default, but can be disabled in the config. There are also options to adjust the delay before the fog damages the player or the damage the fog deals to them.