A level-65 Northropi Vampire neighborhood boss, formerly Viscount Fog's loyal undead-hunting mount.
Sierra was trained by Viscount Fog to hunt vampires and never leave his side. When Fog attacked Miriam, Sierra tried to save him, was injured by the vampire, fled, and transformed within a day into the very creature she hunted.
She attacks Carl above the forest, crushing his chest and legs while trying to pull him apart. Holy Gooper and Donut's light set her burning, but even losing all entrails does not kill her. Carl stakes the detached beating heart with a branch, causing the boss to explode and drop a Neighborhood Field Guide Map.
A giraffe-sized pterosaur mixing pelican and vulture traits, with a lance-long beak, leathery wings, huge talons, and blood-red eyes.
Sierra is the first boss test of the outbreak's anti-vampire tools and heart vulnerability.