4 Players is best. Super Reload, Infinite Ammo, and Instagib will help greatly.You may want to do the sub part alone tuhogh. The bots do a better job with their auto-aim.As for the final boss, the spawning will be different each chapter reload, but it will be the same if you reload from checkpoint. It could be shriekers and guards or just guards.Some say Infinite Ammo or Super Reload will cause even more guards to spawn.Some also say more players mean more guards will spawn.I lucked out with a 4 player party with only headless chicken on. For some reason the guards never respawned after the initial 6 that showed up.So if you seem stuck with infinite guard spawns, try to restart the chapter instead of checkpoint.