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.