Tibault's Will is a Unique Pants in Diablo IV Season 15 for All classes. It comes from General Unique Pool; 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).
Unique power
You deal [15 - 20]%[x] increased damage and gain 25 Primary Resource Regeneration while Unstoppable and for 5 seconds after.
Affixes
Primary Core Stat
Maximum Life
Where it drops
General Unique Pool
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)