The plugins lets you select an area. For every block in the area that has a certain block type it then sets the biome to the biome given. This is useful if you want to make a lake with darker water(Swampland) or an area with a brighter grass texture(jungle). See the video for more information.
Changes all the Water and Stationary_Water in the region to Swampland
This changes every block of the given Type to the given Biome
