The Fatigue Eater

Numenera does interesting things with characters, effort, and health. They're composed of a trio of pools which act as both a resource pool to use to make tasks easier or attacks more damaging, but they also act as health. It leads to an interesting balancing act where the player must make some sacrifices to avoid getting hit with something terrible, and be strategic about when to cast that giant spell. So what if a monster fed off that resource?

Nivunco, level 2 (4)

The nivunco, or fatigue eater, is a dangerous predator in the Ninth World. Unwelcome in city and wilderness alike, it takes the form of a gaunt, man-sized quadruped covered in long dark hair. It crawls on it's belly on four long limbs, moving in an unpleasantly human manner. Its long body lacks a discernible head, terminating in a hairless snout which writhes and twitches as it sniffs out its prey. 

A fatigue eater has a two-part diet, psychic and physical. It feeds off the fatigue an organism experiences, picking it up as psychic static from miles away. Once the nivunco locates it's quarry it will ceaselessly hunt it down. In many cases the creature will let itself be seen before attacking, heightening the paranoia and stress the quarry feels.

However, the creature's tracking ability hinges on the quarry's fatigue. If the quarry were to remove the fatigue, by sleeping or completing whatever task is so testing than the nivunco would have nothing to track. The greater the stress the more nourishing the nivunco finds its prey. The more psychic distress the prey releases the stronger the creature gets. It's physical and mental capabilities increase in step with the diminished capacity fatigue brings. For every 3 points a  PC spends from their pool, for any reason except damage, the nivunco's level increases by one.

When the fatigue eater has sufficiently softened its prey through harrying tactics it goes for in for the kill. It grapples its quarry with its gangley limbs, beating them into submission with its blunt claws. When its prey has collapsed it uses its long snout to completely drain the body of blood. After sating itself on the lifeblood of its prey it creeps back to its den to sleep off its meal, a process that can often take years.

Motive: Food
Environment: Any wilderness, especially high moors
Health: 12
Damage Inflicted: 3 points
Armor: 0
Movement: Short
Modifications: Tracks at level 7, all other tasks involving their quarry at level 5
Interaction: The nivunco is little smarter than an animal, but telepathic communication is possible. They are simple creatures and could be thrown off by mental effects.