Returning player needs some help!
My standard advice for feeling nigh-invincible in PvE: Reaper. That means making a necromancer to 80 (which you already have) then unlocking a number of hero points (1 per location in old world, 10 per location in HoT) to fully open the elite.
If you are NA I can escort you to various hero points in HoT. You’ll just need to unlock gliding and bouncing mushrooms as masteries, which won’t take long at all — do the intro story that starts in Silverwastes, find one mastery point to commune with, and do a couple of event chains.