I made a post about it not working on Biting Winds, but I've tested more weapons and none of them work. Health regen does not proc no matter what. I didn't see this in known issues so I made another post. Edit: more tests. It works on groups of shanks but not groups of dregs, vandals, or captains. Idk if it's enemy type or extremely patchy activation. Just to be extra specific I used Biting Winds, Whispering Slab, Arctic Haze, and Hollow Words. None of them could consistently activate the perk when killing groups of 3 or more enemies in pve. Honestly didn't have the patience to test in pvp since none of these are meta for dueling. And my one slab kill I wasn't hurt beforehand lol.