Temerity is a Unique Pants in Diablo IV Season 15 for All classes. It drops from Harbinger of Hatred.
Unique power
Effects that Heal you beyond 100% Life grant you a Barrier up to [80 - 100]% of your Maximum Life that lasts for 8 seconds. You may now drink your Healing Potion while at full Life.
Affixes
Primary Core Stat
Maximum Life
Where it drops
General Unique Pool
Harbinger (Lair Boss)
Harbinger of Hatred (Greater Lair Boss, 1x Greater Lair Key) - dedicated multi-class Unique
General Unique Pool - every Lair Boss (Initiate, Greater, Exalted, Belial) can drop it in addition to their dedicated table (one guide's Boss Loot Table Cheat Sheet)