Three word IBSFA monster creation with the words echolocation, void, and hound.

The Void Hound is a creature that inhabits the same sub-realm of the Sirent. Unlike the Sirent, the Void Hound is physically weak and vulnerable to any kind of attack, however they are very fast and agile and tend to run away from danger.

Despite this the Void Hound is carnivorous and boasts incredible hearing, being able to locate moving objects at long range with echolocation and then closing in to pinpoint targets by the sound of the beating of their heart when the targets try to hide against the terrain. To kill targets the Void Hound forms a symbiotic relationship with a larger, more deadlier creature, leading it to victims and taking any scraps it can find.