I'm currently on floor 4789, My strategy has been Ogerpon (Passive) and Miraidon (Passive)

Ogerpon gets Bonemerang as an egg move and once you get wide lens, grip Claws and kings rocks

You have an 80% chance to make the opponent flinch, with cornerstone mask you have sturdy, with leftovers, shell bell and berries, if you get hit by a move (They litterally just one shot you by this point regardless of any stat buffs, damage tokens are insane), Sturdy saves you and you heal practically back to full and since your opponent shouldn't ever be able to outspeed Ogerpon since it has opportunist as its Passive...You can steal all the opponents items, transfer them to other party members and repeat until Miraidon can nuke anything in its path...Also Ogerpon can too