Use Molt [Vigor] + Madurai operator focus tree for that extra 85% STR boost that already almost max slow
[Quick Thinking] is your survival mod because you're gonna spam your 3 non stop for fast reloading your weapon with blood forge, 2 augur mod for shield gating which you can also cast 1 / 4 for that invul + shield
I use PSF instead of Unairu because i'm using Madurai for that extra 40% Str buff

Additional note* you can swap out [Blood Forge] for [Dread Ward] which is a good skill for immune, but you need to swap out Transient fortitude for other STR mod, intensify is also viable with around 80% +- slow is good enough (for this if you want to compensate the lower STR you can use parazon kill mod ([Power Drain]) for the max slow.