(Partially written by The "Talk to Transformer" AI as an experiment. I will not be continuing it, but I thought what I do have should be shared.) There is an ongoing war between the Endermen and the Zombie Pigmen. They are both fighting for control over the other mobs and until recently the Endermen had a natural advantage in this battle. The Zombie Pigmen have been experimenting with different diseases and compounds, for example, erythroid infestation and Lyme disease. The Zombie Pigmen are trying to get these fungi into the water supply and in doing so cause the other mob's immunity to prevent it from being poisoned. At the present moment the Zombie Pigmen have used this first tactic, and are controlling the zombie pigs in the Thames water supply. If they succeed in this they will cause a huge infestation and remove the first line of defense for the Endermen.