To defeat Zhalk on the Nautiloid, you will need to pray your Mind Flayer ally can actually land some decent hits. After that, you should recruit Shadowheart, who will be your best damage dealer. Make sure to spec her into Necrotic Touch, as that will be your main damage method. If you can get a few high rolls, while the Mind Flayer can land a few attacks, you can kill the boss. It may take a few tries to get tthis to happen considering low dice rolls and poor Mind Flayer RNG. Remember to loot the devil and escape the ship so you can get one of the best Act 1 weapons before getting to the Nautiloid terminal.