The Avemetrus was a rare blue-green magical creature which looked like a fish crossed with an octopus. It had squid-like tentacles emerging from its back and three sharp scaly spikes on its head and neck. It also had two clawed hands, sharp teeth, glowing green eyes, and walked upon two pointy feet. According to Lao Shi, it is as old as time itself.
Jake and company initially encountered it at the Magus Bazaar, or more precisely in the flea market. It later reappeared in the warehouse district of New York City where Jake and Haley finally defeated it.
Like most magical creatures, the Avemetrus had super strength and above normal agility. However, its most devastating power was its ability to suck the youth out of other creatures. It did so by wrapping its tentacles around its victims or simply by touching them with the suckers at the tips. The Avemetrus' tentacles would glow blue while it was transferring its victims' youth to itself. The longer it kept its victims in its grasp the more youth it would extract from them. Those who were preyed upon by the Avemetrus would not immediately age. It would take a few hours for the body to reflect the missing energy. In this fashion, the Avemetrus was able to live for as long as it could find new and youthful victims to drain.
In order for the victims to recover their true age, the Avemetrus had to be vanquished. Jake managed to do so by forcing the Avemetrus to suck its own youth. Caught in a never-ending paradox, it blew up in a puff of smoke, leaving behind pieces of its slimy skin and guts. Should its victims be nearby, the released stolen energy would make its way back to where it belonged so that the afflicted would instantly return to normal.
- Though the Avemetrus seemed heavily based on marine animals, it was never seen in the water.
- The Avemetrus was vulnerable to fire.
- Lao Shi mentioned that the Avemetrus was too powerful for him to defeat alone.
- The Avemetrus was shown to suck the youth of six individuals:
- Jake turned about 21
- Trixie and Spud turned about 80
- Lao Shi turned somewhere near 100
- Fu Dog displayed no noticeable difference
- Haley was also attacked during their final fight
- However she and Jake defeated it before any noticeable change in her age could occur.
- Haley called the Avemetrus a "squidiot".
- The Avemetrus was sensitive to loud noises and became confused if exposed to too much at once.
- Although octopi and squids usually have between eight to ten tentacles, the Avemetrus only had five.
- Like the Avemetrus, the Krylock was another beast which also had to be destroyed in order for the effects of its venom to be reversed.
- Even though Lao Shi, Spud, and Trixie glowed when their energy returned, Fu Dog did not. This may have been because he was already an aged Familiar with a long lifespan.