||Cave eels resemble large, air-breathing eels, but they have armored snouts and tremendously tough teeth with which they can chew tunnels through rock. They wait in these tunnels for potential prey to walk near, then lunge out to take great bites from whatever’s in front of them. They usually pick narrow cave passages for their ambushes, where prey has little room to back out of reach of the cave eels’ long, sinuous bodies.
These unusual creatures have even been known to chew burrows
into earth elementals and stone golems and take up residence in those
constructs, to the mutual benefit of both. They don’t collect treasure
for any purpose, but because they drag the slain bodies of their victims
(including unfortunate adventurers) into their tunnels to eat them, treasure
can sometimes be found if one follows their tunnels to their lairs. Cave
eel tunnels are just barely big enough for an unarmored human or tiefling
to squeeze through; halflings, gnomes, and elves have an easier time of it,
while dwarves, half-orcs, and dragonborn are too big to fit.
From 5th Edition Foes (Necromancer Games)
A typical encounter involves a cave tunnel where the eels can lunge out and strike targets along its length. Cave Eels lunge out from their burrows and attempt Grab on any targets. They then try to drag them back into their burrows. While doing so, the cave eel may use the gripped body of their opponent as a shield when retracting them into the burrow.
Cave eels conceal their burrows skillfully, so they have tactical advantage on checks to be hidden at the beginning of an encounter. An attacking cave eel lunges from its cave, bites a victim within 5 feet, and then withdraws back into its burrow
without triggering an opportunity attack. While in a burrow, a cave eel has three-quarters cover. The only way to negate this benefit is for a character to ready an action and attack the cave eel with a reaction as it extends its body to strike.
#APPEARING Group (2-5), Swarm (4-24)