It only appears in the episode "Young at Heart" of Season 2 where Jake, Spud, and Trixie first encounter it in the Magus Bazaar (more precisely in the flea market). It later reappears in the warehouse district of New York City where Jake and Haley finally defeat it.
Like most magical creatures, the Avemetrus has super strength and above normal agility. But its most devastating power is its ability to suck the youth out of other creatures. It can do so by wrapping its tentacles around its targets or simply by touching them with the suckers at their tips. The Avemetrus' tentacles will glow blue when it is transferring its victims' youth to himself. The longer it keeps its targets in its grasp, the more youth it sucks out of them. Those who are preyed upon by the Avemetrus will not immediately age; it may take up to a few hours. Thanks to this power, the Avemetrus is able to live for as long as it likes.
In order for the victims to recover their true age, the Avemetrus must be vanquished. Jake manages to do so by forcing the Avemetrus to suck its own youth. Caught in a never-ending paradox, it blows up in a puff of smoke, leaving behind pieces of its slimy skin and guts. Its victims will then instantly go back to normal.
- Though the Avemetrus seemed heavily based on marine animals, it was never seen in 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 (due to not being in contact long enough)
- 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 and 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.