Base magic res (not just immunity) is pretty common.
You can find the full list per act here:
https://www.theamazonbasin.com/wiki/index.php/Act_1_Summary_(Hell)
https://www.theamazonbasin.com/wiki/index.php/Act_2_Summary_(Hell)
https://www.theamazonbasin.com/wiki/index.php/Act_3_Summary_(Hell)
https://www.theamazonbasin.com/wiki/index.php/Act_4_Summary_(Hell)
https://www.theamazonbasin.com/wiki/index.php/Act_5_Summary_(Hell)

And on top of that, the unique bonus ‘Mana Burn’ also gives +20% magic res on top of the base MR. (This can roll randomly on any unique, but also all mobs can get it from the TZ bonus).
Also Ubers and colossal ancients have 75% MR.

It doesn't take much MR to make -% much more effective than +%
And like any other build, you always better optimize your dps to achieve faster kill speed vs immune/high res monsters against your type of dmg, because those targets are what tends to slow you down.

This post was edited by SinsOfTheSun on May 26 2026 10:11am

Fohdin always sets Magick rez to 0 so there's that

its not but renewed black cleft can have either 15% magic or -10% res

15 is bigger than 10

anyhow, the -10 res is likely still better for most areas