I have a 2/30/20/30str/Ber'd Diadem hat that I'm using, but FF seems cool. Does + Fire skills add to CE?
CE is only affected by Fire Res and DR%.
+% fire dmg has no effect on it.
So 15 fire pen is the best increase you can get form helm slot.
FF is by far the best option, as it increase CE by +3 (it's tagged as a fire skill) and gives the max fire pen amount you can get.
But it also fixes the malus you get from fire sunder (you should use it), the malus your merc has on andy (so you can socket it with a 15/40ed instead of a 15/30FR), and it makes all your summons immune to fire (the main thing that normally kills them).
You really don't care about improving any other skill than CE... maxed amp already has a huge radius, your summons are just a meat shield, it's all about your merc's dps to get a first corpse from amp + telestomp, then casting CE with as much -FR and -DR you can get.
CE nec is my favorite build of all time
Sadly, the dmg of CE does not scale with the bonus hp mobs get per player... It always deals:
35-60% Fire
35-60% Phys
and this % is based on the corpse's HP on p1
You get -85% fire res from merc's infinity (-17% vs fire sundered) and 20 fire pen from FF + facet x%/-5 in Homunculus
And you get -100% DR from amp
This is enough to make you
almost always kill the whole screen from 1 CE on p1
But mobs getting +50% base HP per player means that your clear speed drops a lot per extra player, contrary to most builds who can achieve absurd overkill dmg for the purpose of playing p1.
Not just for CE, but also for your merc's capacity to provide a corpse instantly on telestomps.
So... it's really not optimal if your goal is to reach 99.
But it's definitely more enjoyable (and safe) than PSN nova hahaha
D2:R