Instead of 50% reduction to all, their damage reduction will now be 25% to all damage. "Tough" mobs will be 40% to physical damage only. Note that in Nightmare and hell, these can stack for 65% physical reduction. Plus stack with Juggernaut

Not so nerfed part: phased mobs' damage will not be reduced anymore.

Thats nice, phased mobs are the ones I hated the most because it just takes so long to kill them, annoyingly long.