Endgame build that I have been using for a while, easily killing anything in mayhem mode 3. Focusing on the orange and blue trees, but still getting that "unlimited ammo" from the green tree.
Flakker will be your main ad killer. Get one as soon as possible! You can use any other weapons but this build benefits splash or incendiary weapons.
In terms of equipment, you will be wanting the Transformer shield (guaranteed drop from Typhon's bot side quest,) Deathless relic (random drop,) and the Bloodletter class mod (random drop.) An electric grenade mod is a necessity as well.. (I use quasar.) If you want to stay alive always have a grenade on an enemy, the sustain will keep you alive.
Iron Bear is used mainly as an escape tool, so use when you're about to die!