When construction equipment breached the ancient creek bed upstream, it disturbed more than spawning grounds - it cracked open a forgotten burial chamber where indigenous shamans had been laid to rest centuries ago. Now the Tributary Mummy rises from waterlogged eternal sleep, using every connected waterway as a highway for vengeance against those who desecrated the sacred waters.

Wrapped in algae-stained bandages that constantly drip creek water, the Tributary Mummy can dissolve into any flowing water and reconstitute wherever tributaries connect to the main creek system. Its presence causes localized fog banks to form as the temperature differential between its ancient cold flesh and warm surface water creates supernatural mist. The creature's bandages trail behind it like aquatic kelp, and its hollow eye sockets glow with the same bioluminescent green as disturbed creek sediment.

The Tributary Mummy serves as a mobile enforcer of ancient territorial boundaries, appearing without warning at any water crossing to challenge those who venture too close to sacred sites. It represents the historical memory of the waterway and escalates encounters by using the tributary network to coordinate ambush attacks during peak fog conditions.