Tips on 3rd boss outlaw difficulty?

[Phetecile]

The melee attacks seem incredibly fast and I'm getting absolutely demolished because of how much damage is being dealt. Would an ice build basically be required for this?

[_notjinxedyet]

ice and stasis work pretty well for stun

(special) lightning rounds on mortar (cursed legendary variant) do upwards of 1.2k damage on hit

[Phetecile]

Beat em with a rifle full of lightning strike and ice bullets
First half is definitely the hardest part