Biomass

Biomass is created when a beckon starts targeting a mob, it appears as a green pyramid like shape with cubes on each side, it slowly grows bigger and proceeds to explode into a parasite. (it will grow bigger depending on what level the beckon is) Strangely, if you were to save the mob and the nbt, it would always spawn the same mob. (You can use the mob battles mod to test this out)