The fictional yrthak resembles a gigantic pterodactyl, the real-life but extinct flying reptile. It is described as 20 feet long, with a wingspan of about 40 feet. It is green in color, and lacks legs, only having wings. The creature has a dragon-like plate at the end of its tail, and a feature akin to a large dorsal fin on its back. The yrthak has a few short spikes on its head, and does not have eyes. It requires a special sensory organ in its tongue to see. Also, coming from its head is a lance-like protrusion known a "sonic lance". The yrthak lives in temperate mountains.
The yrthak attacks by shooting powerfully focused sound waves from its lance. These sound waves are so powerful, they can cause a mountain to explode. The yrthak swoops from the air, blasts the ground with the sound waves, and then the resulting explosion causes piercing damage to those nearby. In addition, the yrthak can also snatch up prey in its mouth and drop it. The lance is said to have magical abilities, and this is the primary reason the dangerous creature is hunted at all.