diablo-3
Sometimes, I see a whirling laser or some enemies chained together by some orange chain: those things kill a lot.
I don't know how much damage they cause, and I don't know what kind of move they pull out against me, but others seem to know that. How do I know? I've turned on every display in the options menu.
There is an option to display damage numbers within the menu configuration options.
By default, it will only show critical damage, but it's easy to make it show all damage.
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The only true way to find this out is testing. You could easily do this on normal.
You should do multiple runs with 0 Resist All to get the control information. I would say a sample size of at least 10 kills. Average the damage from each fist attack (or whichever attack of his you want to figure out) across all runs and that is your control figure.
Once you have the control, you can start introducing variables like each separate Resist stat. I would start with Physical Resist, preferably a very high amount, so you can more easily see the impact it has without the difference falling within the margin of error. Do the same amount of runs and average the damage once again. Technically, if the attack indeed is Physical, you should see a reduction very similar to the amount of reduction your Resist stat is giving you. The more runs you do and the larger the sample size is, the more accurate this will be and the closer the actual reduction you see will be to the amount the stat says it will reduce by in the character sheet.
You will most likely have to spend gold on the proper gear to do this, but it is the way people have found out many of the games mechanics and nuances. FRAPS or some other form of recording is also a good idea so you don't have to write things down during the fight.
This may not be the easy answer you wanted, but it is the scientific method, and it's how humans have been figuring things out for years! Especially theorycrafters in video games!
Best Answer
The affixes you're talking about are Fire Chain and Arcane enchanted. There's no way to tell the exact monster-level, but these two affixes only spawn in Nightmare and later difficulties (see this question for more information about the affixes).
Generally you want to stay out of the arcane "laser-beams" (and yes, they deal a lot of damage), which shouldn't be that hard, unless you're jailed or frozen. You can also break the fire-chains by luring a monster away from the others.