The Pantano Eel is an eel native to Pantano (duh).
Physical description
Pantano eels vary greatly in sizes, from about half a meter at birth to 25 meters (that's a blue whale, y'all) or more—because they never stop growing until they stop living, truly ancient eels are likewise truly massive. They're fiercely territorial and so cannibalistic it's surprising they haven't gone extinct—a given Pantano eel's favorite food is almost always more Pantano eel—but they're also fond of juicy, sentient bipeds, so watch your back.
Recent developments
The Crew of the Cantina Turner used eel bile in an elaborate sabotage of Delta Base and then posed as local plumbers to conduct an even-more-elaborate sabotage (and a prison break). They later lured (and formed a religion around) a giant eel at the Oda Clanhold.
Legacy
A fabled gargantuan eel is said to lurk in Pantano's depths, surfacing to bring either great fortune or great destruction. The oldest references to such a creature date back ten millenia, and several of Pantano's early and more backwater civilizations still worship this great eel as part of or all of their ancient religions. Names for this creature vary, but some popular ones are "Shai-Hulud", the "Midgar Zolom", and "Jörmungandr".
Gameplay statistics
I'm going to use the stats of a Dianoga, that thing that tried to eat Luke Skywalker in the Death Star trash compactor, and that probably did a bunch of other weird stuff in the anime version of A New Hope that Jim watched (and co-wrote). The Dianoga is on page 116 of Allies and Adversaries.
Nonsense
An artist's rendition of an older Pantano eel, but like… using 1996 technology.
Ohhh fuuuck it's coming right for you!