The Neo-Soviet marine biomods
Classified as a category 4 threat, the Elib is somewhere between a vampire lord and Godzilla for limits of escalation. Yes, I would consider using a nuclear device to kill just one. I am that sure that I want it dead.
In a small farming community, the only way to cross a river is to basically pole vault across. A small section of river has a small raft on a string to pull items across but for a person to cross they must use one of the many provided poles. Might be interesting seeing what the players do when they come across it. Villagers do it all the time so are skilled and can do it with ease.