They look like blue crystalline creatures with two very narrow bat wings, a square head with two large eyes, no body besides the wings, no limbs besides the wings, and a very large mouth on the bottom of the Badtulfa, which overlaps the wings. Their wings have small claws on top.
Badtulfas are mean creatures that bite animals, gnaw exposed pipes, and defecate in the air to land on unsuspecting people. They are crepuscular, and only appear in public when it is autumn. The rest of the time, they hibernate in sewers and grottoes. Badtulfas are made of a hard crystal, and can drop onto their prey's heads - however, this gives them a chance of shattering when they hit something too hard.
- They reproduce through their venom. The male bites the female in the back, injecting his venom into her. Badtulfas are immune to their own venom, and so the female absorbs the venom into her bloodstream where it is absorbed into her eggs. The eggs are made of a similar substance to the female's venom, and when it is infused with the male's venom, the two combine to create a fertilized egg, which hardens over a few weeks to become a small crystal. The female drops the crystal onto the ground, where it absorbs nutrients from the soil to grow into an adult Badtulfa.