The Ruiner - Borderlands 3 Farming Guides
Location: Crater's Edge on Gehenna
Part of: Riding to Ruin Story Quest
Drops: Bloom (Jakobs Pistol)
The Ruiner is the final boss of the Bounty of Blood DLC for Borderlands 3. You'll fight this boss in the Crater's Edge arena which is marked on my map in the screenshot above. The best tip I can give you for the actual boss fight is when you follow The Ruiner underground, you can actually stand in the "acid" the platform is lowered down into for a little bit. You don't have to bail before it reaches the liquid at the bottom.
As far as loot goes, Bloom (Jakobs Pistol) is the only item on The Ruiner's dedicated loot list. This item is unique to The Ruiner and is difficult to obtain (or impossible) off of other enemies throughout the Bounty of Blood DLC.