According to the Shadowmoor Style Guide, the boggart warrens have become gangs—loose, semi-nomadic, wolfpack-like social groups. The boggarts seek out new sensations relentlessly, but they also have a strong destructive urge. They hunt with rusty weapons, which have lasting effects on their victims:
Contrariwise, some cards effectively start out already being affected by wither. The reason that Witherscale Wurm treats other sources as having wither is because its skin is constantly sloughing off:
In the sunlit world of Lorwyn, Flamekin Bladewhirl Brighthearth Banneret Shared Animosity used the fire of their own bodies to heat their weapons. The flames of their counterparts in Shadowmoor, the cinders, have guttered, but their bodies still glow warm enough to heat a blade—and what they lack in fire, they make up for in sheer cruelty.