Sewage eel

are fish that are able to spawn hidden in liquids with volume greater than 200 drams (wading depth) like, , and.

When hidden, the eel technically does not exist, but rather a spawning object. This object does not move, and a static amount is generated when the ooze/goo/sludge is created. For example, have an 80% chance to spawn a puddle of  in all tiles adjacent to it, with a 25% chance those puddles will contain a  spawner.

The spawning tile can be searched from an adjacent tile. This happens passively when the creature walks next to the spawning tile, and the creature will have a chance based on their intelligence score to reveal the eel. A random number from 1 to the searcher's intelligence score (including bonuses) will be rolled. If this is higher than or equal to the difficulty of the hidden eel (which is 16), the eel will no longer be hidden. This chance is. This will spawn the eel before it is able to strike.

If the eel is still hidden when the spawner is stepped on, there's a 50% chance that the eel will emerge in an adjacent tile and attempt to trip the creature if the eel is hostile towards it, forcing them to make an agility save of difficulty 16. If the save is successful, the creature will maintain their balance. If not, the effect that will occur upon prone will change depending on the liquid that the creature falls into.