Pack-Viper

Ecology

Pack-Vipers are pit-sensory ambush predators -- the heat-pit organs that line the anterior jaw give them a thermal map of their environment independent of light, which makes them effective hunters in the sealed, lightless spaces that ruin environments produce. They are not socially coordinated animals; the "pack" designation is a field description of denning behavior, not cooperative hunting strategy. They share heat sources and den spaces because the thermal conditions that suit one suit all, not because they hunt as a unit. The encounter dynamic when a den is disturbed is simultaneous rather than organized: every animal in the space responds to the same stimulus at the same time.

The standard Pack-Viper is a small, fast, primarily rodent-hunting animal with a neurotoxic bite that operates on a delay -- the target often moves away before the venom produces its full effect, which for small prey is death at distance from the den and for large prey is several days of degrading physical capacity. The pit viper variant is a substantially larger animal with proportionally stronger venom and enough body mass to take medium-to-large prey: the Poisoned condition it inflicts imposes Disadvantage on attack rolls and ability checks, and the ongoing Constitution saves to clear the venom extend the debility well past the initial encounter.

Both variants prefer substrate-warm environments, and both show the Miasm-thermal correlation that the Constriction-Snake demonstrates -- they cluster in zones of elevated nanite saturation because the thermal byproduct suits them. A ruin level that runs warmer than ambient, with no obvious heat source, is worth checking underfoot before walking through.

Neither variant is aggressive in the sense of pursuing. They bite when threatened, cornered, or accidentally contacted. The danger is not that they want to fight; it is that the environments they prefer make accidental contact easy, and a den of twenty Pack-Vipers in a wall cavity that a character reaches into produces a very different result than a single animal encountered in open ground.