Wendigo Brand is a Unique Ring 1 in Diablo IV Season 15 for All classes. It comes from 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
Every 15 kills in the last [50 - 60] seconds increases your damage by 2%[x], and Attack Speed by 1%[+].
Affixes
Primary Core Stat
Maximum Life
Where it drops
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)