Here’s the Chaos Reap Spirit build.
Wraiths are in fact invincible, so you don’t have to worry about them getting hurt from monsters at all. It allows you to not have to worry about them dying off too early, as they are a massive source of pet damage.
I remember having tried the Desecrator’s Occultist set, but I was largely disappointed at it - it was far too squishy to handle even regular Nemeses, and having only 50% Elemental to Chaos conversion hurts any chances of using that conversion properly.
Thankfully in MC, if you side with Barrowholm, you don’t have to worry about fighting the Reaper Nemesis, as it’s the biggest thorn of any Chaos-related pet build. I like to make sure any of my pet builds can defeat the highest-resistant Nemesis before recommending it to anyone; I know how much of a slog things can get when you just can’t get enough damage to feel adequate with your build.
Speaking of which, I have video of the Lightning hybrid defeating Grava’Thul at SR65, so now I have 4 SR65-66 capable hybrid pet builds that I’ll post once I get the proper screenshots and everything.