Unholy Might is a buff that grants 30% of physical damage as extra chaos damage. Gain X% of Y damage as extra Z damage, such as granted by Unholy Might, is a type of damage conversion. It does not remove the original damage type, and is not limited to 100%.
The effects of Unholy Might are affected by increased Buff Effect. The duration of Unholy Might cannot be increased by the duration passive nodes because these only increase the duration of buffs applied by skills.
PoE 3.19 Changes
Problem:
The Necromancer's Unnatural Strength notable passive skill is extremely strong for almost all minion builds due to how well minion skills scale with gem level. This skill makes it hard to justify using other ascendancy classes for minion builds.
Solution:
Change Unnatural Strength to provide a less universally applicable stat, and allow more access to minion gem levels on items instead (as detailed above).
The Necromancer's Unnatural Strength Notable Ascendancy Passive Skill no longer provides +2 to Level of all Minion Skill Gems. Instead, it now grants Minions Unholy Might.
2% increased Attack and Cast Speed for each corpse Consumed Recently, up to a maximum of 200%
Enemies near corpses you Spawned Recently are Chilled and Shocked
Corpses you Spawn have 50% increased Maximum Life
(Recently refers to the past 4 seconds)
(Killing an Enemy is not Spawning a corpse)
(Shock increases Damage taken by 15%)
(Chill reduces Enemy Action Speed by 10%)