Nemesis Bracers is a Unique Gloves in Diablo IV Season 15 for All classes. It comes from Season 15 Legacy Unique; Legacy Unique: general Unique pool (permanent, Seasonal + Eternal); Horadric Cube: Item Transmutation - Upgrade to Unique from a Common base of the same type.
Unique power
Shrines will spawn an Elite Pack.
Affixes
+Primary Core Stat ([150 - 180])
x% All Damage Multiplier (x[12 - 20]%)
+% Attack Speed ([8.0 - 10.0]%)
+% Movement Speed for 4 Seconds After Killing an Elite (guaranteed affix) ([14 - 28]% (one guide) / [10.0 - 18.0]% (another guide))
Where it drops
Season 15 Legacy Unique
Legacy Unique: general Unique pool (permanent, Seasonal + Eternal)
Horadric Cube: Item Transmutation - Upgrade to Unique from a Common base of the same type
All Unique items can drop at level 1 in any Difficulty since 3.2.1 (official patch notes)
General Unique loot pool / world drop - not attached to any boss loot table (one guide, another guide and a third guide)
Nightmare Dungeons, Helltide Chests, World Bosses, Kurast Undercity, Purveyor of Curiosities (Murmuring Obols) (one guide)
Uber/Lair boss ladders and Tormented bosses, Helltide chests, Whisper caches (one guide and another guide - low authority, unverified)
random drop - not listed on any Lair Boss loot table in the community loot-table cheat sheet this dataset uses; no official Blizzard list confirms it