Arioc's Needle is a Unique Polearm (Two-Handed Slashing) in Diablo IV Season 15 for Barbarian, Druid, Spiritborn. It comes from Craftable as Unique Charm as of 3.2.1; World drop (dungeons, Helltide, Pit) - one guide / another guide; Horadric Cube: Item Transmutation - Upgrade to Unique from a Common base of the same type.
Unique power
Gain 50%[+] Deadly Strike Chance. Your Deadly Strikes deal [70 - 100]%[x] increased damage.
Lucky Hit: Up to a 40% Chance to Deal Poisoning Damage over 10 seconds (guaranteed affix) ([2,200 - 5,400])
Where it drops
Craftable as Unique Charm as of 3.2.1
World drop (dungeons, Helltide, Pit) - one guide / another guide
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)
Waking Nightmare Prime Evil encounters (Capstone Dungeon Waking Nightmares; rarer from minor Nightmare bosses via Chronicles of Nightmares) - one guide