rifle

this requires box fishing, but i used it to win.

1911, pack a punch to mustang and sally. Use it to make crawlers so you dont have to focus the zombies as much.

PKM, pack a punch. Use it to dump into the boss

Any LMG like the raw, hades and PKM will dump pretty big damage to him. Any gun with a grenade launcher or mustang and sally are useful for clearing out enemies.

MG08/15 never fails, ever! Get double tap perk, PaP the goat LMG and you have a massive damage dealer with a very reasonable ammo reserve and swift reload even without speed cola. Plus you have practically infinite ammo on the table for only 150bucks, even if it's a packed gun.

Use any repacked gun with thunderwall, turned or blast furnace to deal with any hordes distracting you, so you can focus taking down the boss.

If you are rocking mule kick, then grab for a third weapon one of the powerful magic maces, they'll be a huge help in a bad situation. They are unpackable, but still a major aid in the fight.

Grond staff is your best friend for AoE/knockback for keeping zombies away. Then the rifle right by the starting box is pretty good packed, and you can pack it early by finishing those starting objectives. I usually keep that one the whole game, and maybe grab an LMG, don't recall the name but there's one that is two sides like the mustang and sally that deals lots of damage really quick. Ammo isn't an issue, but having Grond is nice to give you time to get more.