I Killed 100 boneshatter on level 46 with 14.9% luck skill.
My findings:
66% of the drop were Common(This includes potions)
23% of the drops were Uncommon
3% of the drops were Rare
4% of the drops were Epic - All 4 epic drops were Hoop of the Two Knights. Which makes me think that 46+ means you can't actually get it on 46. I'll try again once I get to level 47.
4% of the kills did not give anything.
EDIT: it took me 4 kills to get Boneshatter Animus after reaching level 47.
https://nwdb.info/db/item/ringt4_hoopofthetwoknights 3rd and 10th kill
Respawn: ~3 mins