The Neptunium Golem fight comes right after Helvius, which does not require any more preparation than the Helvius fight due to their similar difficulty. The Neptunium Golem drops a single Neptunium Ingot which is one of the ingredients to the Neptunium Pickaxe. The Neptunium Golem can be summoned at a Summoning Station by using a Neptunium Crystal as the ignition. Using a Cosmologist villager is recommended to replenish your supply of Neptunium Crystals. You can choose to do this fight first or you can choose the Dreadknight. The Dreadknight doesn't drop any ingredients to the Neptunium Pickaxe. However, it drops a whole new set of armor (Bloodsteel) and a Dread Blade. The Bloodsteel set is superior to the Neptunium Set and will carry you throughout the rest of the game. The Dreadknight can be summoned at a Summoning Station by using Guardian's Flesh as the ignition.