Champ of Balth
I tried to soloed him once on a core necro, messed up when he does his OHKO attack and forgot to get up on the ledge though so I wiped, and when I came back I couldn’t lose his aggro after killing the hounds to heal up.
What I did the first time though was I tried to aggro the hounds while he was aggroed on my flesh fiend. Then I ran into the back and hopped up on the ledge, using staff to kill the hounds, luckily my flesh fiend kept the avatar’s focus long enough for me to full heal and resummon my blood fiend. After they are dead its actually a really straightforward fight on a necro, didn’t have to dodge much tbh. Staff and shroud are your friend, and remember that his OHKO attack starts when he hits 50% health. Signet of Locust also helps, move speed is nice and its an emergency heal if you need it. And remember that Shroud 4 gives you a decent chunk of life force back as a core necro, so use it to just eat large attacks if you need to.