Plague Engine

Little is currently known of Plague Engines, as few exist. The Gods have discovered some key strategic information about their purpose: that they are great and terrible beasts, that mutate the Rot Plague into new forms. Each Engine has its own special mutated variant of the Plague that it unleashes upon the world. 
The world is divided into 18 land regions and 18 aquatic regions, each keyed to their own Engine. Once a region is infected enough by other strains of the Rot Plague, a larval possible-engine will form and will seek a place to safely grow. Plague Engines have magical ways to avoiding detection and blending into their surroundings, though these powers remain under-studied and poorly understood. Once a larva has found its nest and established reached basic viability, it will become an Engine - all other larvae in that region will burrow into the ground and become channels, infected nexii that speed up the growth of the main larval engine. 
It takes about a year for Engines to grow, though channels and mass infection can speed up that process. Engines do require a large number of infections in their region to develop. If infections taper off or stop, the Engine will not grow and the timer will halt. Prolonged failure to accelerate infections will force the Engine into hibernation. As the Engine grows, it will slowly begin emanating its new strain of infection - but will wait until it is finished growing to fully unleash it. 
Once an Engine has finished growing, it will be a massive monster (we may call it a "kaiju", to indicate its enormous size and city-breaking potential) - though it may wait until Kasmir, the Rot or its attending Plague Warlocks deem it safe to show itself. 
While an un-camoflouged Plague Engine is more vulnerable to detection, it is also better able to move around and defend itself. The full ability of the Engine to defend itself is not fully understood currently, but it seems likely that the Engine can create regional environmental effects and some kind of monstrous hazards - though how those work are, again, unknown.
Each Plague Variant can spread outside of the Engine's territory, but Aquatic and Terrestrial plagues stick to their respective sides of the land-sea divide.
Once a Plague Engine is dead, it cannot be revived.
Currently, there are several plague engines known:

• A large shellfish-like engine in the Kingdom of Orpora, slain by the rebel forces of Longshore Reef and the hero Makar. Aquatic. Strain unknown.
• A Leviathan-like Plague Engine in the tropics. Aquatic. Strain unknown.
• An Engine of unknown shape in Vikasha. Terrestrial. Unleashed the Vermin Rot Plague.
• A Dragomander-shaped engine in Kreniko. Currently fighting the God Squad (Makar, Kipilu, Arzet, Potha). Strain Unknown. Terrestrial.