Update 3:
It’s the penultimate week for Borderlands 3’s 10th Anniversary Celebration. Not only will Gearbox be dropping the limited-time Bloody Harvest Halloween event later this week, but there will also be the “Mayhem on Twitch” event to celebrate the fourth week in Gearbox’s five-week celebration.
During this event, any player who enables Mayhem Mode will have an increased drop rate for Anointed Gear, along with extra XP for defeating enemies, and reduced values for various Mayhem Mode penalty modifiers.
Mayhem Mode is unlocked by finishing the main story for Borderlands 3, so these rewards will be locked to you if you haven’t finished the main campaign yet.
Source: IGN.com Borderlands 3's Ongoing Anniversary Event Now Has 100% Win Rate for Rare Chest Events