The Spirit Realm

Quite possibly an old ensnaring concoction - if a mob's snared and in "run away due to low health" mode it'll just stand there. The exact details vary according to snare percentages.

There are root "potions" out there, but nothing that we can make AFAIK.

http://lucy.allakhazam.com/item.html?id=25648
http://lucy.allakhazam.com/item.html?id=10261
http://lucy.allakhazam.com/item.html?id=14316

etc.

There is this - http://lucy.allakhazam.com/item.html?id=3820 - but its a snare, not a root.

Also from crystal caverns there is http://lucy.allakhazam.com/item.html?id=25648 which is a root, but has no entanglement in its name.

There are several others but none that are made with alchemy that I know of,

So in answer to your question, I think it was 'probably' looted rather than made