posting this as no one has said a thing about this items in 10+ years (lol).
One dropped for me tonight in Dragon Necropolis. I killed about 15 entropy serpents as I was hunting around. I imagine it would have taken me 150 kills or more if I had been trying to get the drop (I was just scouting out looking for named rats).
Depending on how you use this item, it could be some scary fun. I miss the ancient UI pic as shown here (been years since my EQ looked like that), but it remains accurate as to the items stats.
entropy serpents live in the water puddles amongst the Chetari (rat men). Usually you get 2-3 on a pull and they aggro from pretty far off. Careful hunting if you are lower level.