Consumptive Mass

From publisher blurb:

The precise origin of these abominations is unknown. Some theorize they may have begun as Otyughs which transformed after exposure to the waste products of some mad wizard’s experiments. Others believe it arrived directly from the far realms or the planes of chaos in some larval or seed-like state. Whatever its source, its numbers continue to grow and spread across the material plane like a plague of slugs.

This Monthly Monster provides all the lore, tactics, and stats you need to run it in your game, and provides inspiration for a slow, creeping threat for your players to deal with.