The Mutandis Extremis is an item from the Witchery mod. This item is an upgraded version of Mutandis. It can mutate multi-staged plants like Wheat, Cactus, and Sugar Canes. Mutandis Extremis can also turn Grass Blocks into Mycelium, and underwater Dirt blocks (and the dirt around them) into Clay blocks. Mutandis and Mutandis Extremis are the only way to acquire some Witchery plants, like the three magic trees, Rowan Sapling, Alder Sapling, and Hawthorn Sapling. Mutandis Extremis can transform cooked meat into other cooked meats, like Mutandis. It is used in several Witchery crafting recipes.
As of Witchery 0.21.0, custom plants added by other mods can be added to the mutation list through the config file.
This information pertains to an older version of the mod.