Wyrsa are incredibly deadly creatures that can be conjured by spell. A mad cross between a viper and a coursing-hound, they hunt in packs, taking down their prey with stunning efficiency. They appear to flow, more than move like a normal animal. They have poison fangs and talons. As they are described:
"In color they were a smoky black, with skin that gave an impression of smooth scales rather than hair. They had long, long necks, too long by far, and arrowhead-shaped heads that were an uncanny mingling of snake and greyhound, with yellow, pupilless eyes that glowed in the same way and with the same shifting color that the globe that had birthed them had glowed. The teeth in those narrow muzzles were needle-sharp, and as long as a man's thumb. They had bodies like greyhounds as well, but the legs and tails seemed unhealthily stretched and unnaturally boneless." (Magic's Pawn)The wyrsa were originally created by a Sorcerer-Adept who predated Ma'ar. Analogous to the kyree, the Adept designed them to be more formidable guard and hunting dogs. However, they couldn't be controlled and they eventually escaped their creator long before the Mage Wars. Urtho's gryphons used to hunt them in pre-war days, as they ran in packs in the wild in some places. Fortunately, they only had a couple of offspring at a time every two years, so they did not procreate as quickly as some creatures.
Tadrith and Silverblade were attacked by a pack of Changed wyrsa while en route to their first field assignment with the Silver Gryphons. Those wyrsa were larger and more intelligent than normal, colored a very dark black that made them almost impossible to see at night. They also twined around each other, leaping and twining to induce a trance state in any watching enemies. They were the twin offspring of a single Changed female who was the pack's leader. Unlike other wyrsa, these fed on magic. They stripped the magic from Tadrith's carry-net as he flew overhead, causing the pair to crash in the wilderness. They continued to stalk them through the forest, killing most of a rescue party sent to retrieve the two. Eventually, with the help of Skandranon and Amberdrake, they managed to wipe out the pack.
Tylendel called up a pack of wyrsa to attack the Leshara family as part of his mad scheme to avenge his twin's murder. Gala tried to intervene, choosing death-by-wyrsa over her own grief. Evan Leshara was also killed before the pack could be trapped and destroyed.