was on lunch break on my phone decided to something very easy, killing tzhaars as i still need all their drops, got ring of stone in 100-200 kills which is a 1:5k drop rate.
the main way to do tzhaar drops is to kill the ones in city as by the time you get ring of stone you should have all other drops already done. for me this was the first drop i got lol
i will be doing cauldren for the other drops as drop chance is so much higher