Tips
Remain mobile. Grapple. You can re-grapple to a previous grapple point without touching the ground as long as you grapple to another point first, then aim back at the previous.
Staying mobile and on the air is the easiest way to avoid getting pushed off and sniped by kreeps.
Use
Incarnate a bit after you're done with crystals and orbs, unless you need it for more damage during that phase.
Weapons & Usage
Goes without saying: use repkit for Amp and
Blood Shot before using any big burst of damage.
Use
Torgue AR/
Potato Thrower IV 'Airstrike' underbarrels for Crystal Phase. Once for crystals, once for orbs.
- This requires Head Ringer
Torgue Enhancement. With an additional splash radius boost on top of that, it can be enough to end the Orb phase with the Airstrikes too instead of having to use
Darkbeast. - Alternatively, use Airstrike once on crystals then swap to a
Darkbeast to finish off the orbs if you don't have enough radius boosts. - Another choice is
Linebacker, which can be excellent for both crystals and orbs.
For the remaining phases:
Maliwan Shotgun 'Beam Tosser' underbarrel is excellent. Ideally fire through the boss so it hits as many times as possible then bounces back for more hits. Other options for damaging Bloomreaper include the
Jakobs Shotgun 'Spread Launcher' or
Oscar Mike 'Space Laser', alongside other potent underbarrels you may have.
For the final phase after immunity,
Maliwan Shotgun 'Beam Tosser' is still great, but if you don't have another, the
Jakobs Shotgun 'Spread Launcher' or
Oscar Mike 'Space Laser' can usually finish the boss off.