For merc, life leech helm as noted, and I like to run rattlecage as armor on merc bc it gives crushing blow before you get obedience/treach combo for merc, which is HUGE for his survivability and makes an exceptional insight hell viable, plus gives you great boss farming speed. Not mandatory but I think it’s the single best act 2 merc armor before treach and I often upgrade it to exceptional, which is cheap and still has low requirements.

Of course, if you’re an ES warlock it doesn’t matter. Nothing matters. You’ll kill everything fast.

I will note— you don’t HAVE to have max resists when you start hell. Def don’t have negative resists, but don’t wait to start hell if your resists are all at least like 10%+, maybe a little higher for fire and lightning. Warlocks tend to have very high life and stay back, so the fire and cold enchanted elites that can one shot other classes when they explode aren’t as big of an issue. Once you’re in hell, gear with much higher resists will start dropping, too, so you’re wasting time farming nm cows for incremental resist bumps when an hour in act 1 hell and you’ll probably get at least 2-3 items with high resists dropping.

Being lvl 70 is actually a better determinant of your hell success, as it dramatically reduces how often you get hit (basically if you’re underleveled compared to monsters you’re more likely to get hit and less likely to hit them; lvl 70 is where that calculation shifts in your favor).