The legendary item “Oath of the Sustained” has a lifesteal effect when damaging enemy health, however damage from some sources does not trigger the lifesteal. Two examples I have tested are Ambra’s Radiant Halberd mutation for her alt attack (I haven’t tested the regular alt attack yet) and Caldarius’ ultimate ability Aerial Assault. I know that both of those abilities have potential built-in lifesteal effects (in the form of a helix upgrade that is mutually exclusive to Radiant Halberd for Ambra and in the form of his character-specific legendary item for Caldarius) which may be related, but Thorn’s Volley also has a potential built-in lifesteal and it works fine with the item in question.
Oh, a abilities as well? I thought this only worked on base attacks. I wonder if this stacks with the Leechsteal Brooch then… Been farming Hylis to no avail, I want them both