Sky Bullies - Borderlands 3 Farming Guides
Location: The Anvil on Eden 6
Part of: Crew Challenge
Drops: Hex (Grenade Mod) and Rebel Yell (Atlas AR)
Sky Bullies are a Target of Opportunity/Crew Challenge found in The Anvil on Eden 6. You'll find these enemies about midway through the zone just off of the very large room that also leads to the Anointed Alpha enemy. The Sky Bullies are one of the few Crew Challenges in this game that consists of more than a single boss.
As far as loot goes, Hex (Grenade Mod) and Rebel Yell (Atlas AR) are both on the Sky Bullies loot list and neither of these two items are unique to them. What that means is the Sky Bullies only drop them more commonly, they don't hold a monopoly on the item.