Cheese it with healer teams or destroy him with the power of powercreep.
The old strat that I used on release was healers where you bring all the healers you can fit on a team to stay alive, like 4 healers plus something that can deal damage and not die. The downside of this strat is that you'll possibly spend all day doing this because it takes 30+ runs and if you fuck up the timings or let your healers die then you're fucked considering the idea of this strategy is death by a thousand cuts slowly chipping away at its HP doing like 100k or 300k damage per run.
Else you can slam its face with powercreep if you're strong enough. Something with Laby will probably work if you can make a proper team with her but I haven't tested it myself and have no chance of testing it myself because I'm at the endgame and anything I toss at it will melt its face off.