Penitent Greaves is a Unique Boots 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 are permanently Unhindered and leave behind a trail of frost that Chills enemies. Your Chill effects cause enemies to take [10 - 15]%[x] increased damage from you.
Affixes
Primary Core Stat
Movement Speed
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)