The Spitfish!

Spitfish are aquatic creatures that undergo radical morphological changes over the course of their long lives. The Young and Mature forms travel in schools, able to live in salt and fresh water both. A school of Spitfish are all born from the same Elder Spitfish. Schools of Spitfish in freshwater often 'nest' for d6 days at some point near the waterline before moving on. Spitfish feel threatened by the presence of animals at the shoreline or in the water near to their nests, but will target fires in range preferentially.

The common school of Spitfish tend to cluster together at the shoreline to launch a volley of spit attacks at a target and then retreat to deeper water for 10-60 seconds. If the threat remains in range from the waterline they will repeat the process until they've exhausted their spits/day, have been chased off, etc. A common school of Spitfish will contain 3-12 Young Spitfish, and 1 Mature Spitfish per 6 Young Spitfish.

Young Spitfish can spit a small jet of water to a range of 15', 5 times a day. The spit attack of a Young Spitfish does no damage, but 3-12 simultaneous jets of water at the same target can be enough to douse/extinguish small fires, soak a dwarf, etc. The Young Spitfish are very small and tend to disperse and reform quickly. They are in every other way identical to other small eels.

Mature Spitfish have developed the ability to store more water and eject it with much more force. The water they spit is stored in a special organ which also infuses this water with a caustic slime. The range of the Mature Spitfish's ranged attack is 20' and they do not target fires. Targets hit by the ranged attack of a Mature Spitfish take d6 damage (save for 1/2 damage). Mature Spitfish generally do not attack the same target that any Young Spitfish present are attacking - unless, of course, there is only one target. The Mature Spitfish are otherwise identical to regular eels.

Old Spitfish travel in pairs. There is a 75% chance that an Old Spitfish pair travel with a school of 6-24 Young Spitfish, with 1 Mature Spitfish per 4 Young Spitfish - otherwise the pair is unaccompanied. An Old Spitfish couple always work in tandem and communicate through weak electrical pulses. Old Spitfish only come to the surface if the school they accompany is hard pressed or has been highly agitated by the presence of something on shore for more than thirty minutes.Old Spitfish have a small pebble (injested as a Young Spitfish) which has worked its way to the bone between its eyes. The Old Spitfish Stone radiates constant darkness 5'R. The spit attack of the third phase of the spitfish is more caustic than that of the Mature ones, and additionally holds a minor charge (2d6 damage). The spit attack can be used one every two rounds. If Old Spitfish come to the surface, they stay there until the threat is dealt with. If one of them is killed, or otherwise stops attacking, the other will go underwater. Some fisher-legends say that the Old Spitfish grant wishes. Should this prove to be true, the chance of capturing such a specimen should be 10% at best. In such a case, the Old Spitfish should probably be able to speak and live & breathe in air (at least while in duress), and would extract an oath to release them and never harm the Elders (the Elder Spitfish). Otherwise Old Spitfish should be treated as large flounders.

Elder Spitfish do not travel with others of their kind and pay no attention to the shore. In tactical situations, an Elder Spitfish should be treated as a large/giant squid with only 4 tentacles. Elder Spitfish spend half of their time wandering and half of their time in nest. While wandering they are voracious, powerful underwater hunters. The presence of a passing Elder Spitfish in a small lake might be noticed when it rapidly destocked. A nesting Elder will digs long tunnels down and if the body of water is small enough, a dip in the water level may be noticed. Nesting Elder Spitfish dig very long tunnels with acidic secretions from their tentacles, and these sectretions should also increase the damage delivered in combat. At the end of an elder's nesting period, there's a 50% chance that hundreds and hundreds of Spitfish eggs have been deposited in the tunnels, producing a huge 'bloom' a few weeks after the Elder departs.
The Spitfish Stone found in the Old Spitfish skull has become an accertion of them in the Elders.
This larger stone produces 10' radius darkness. It is also supposed to be a potent ingredient in some magical/alchemical formulae. Elder Spitfish will eat other Spitfish that are not themselves in the Elder form.

Young (minnow)
Mature (eel)
Old (large flounder)
Elder (large/giant squid)