The Eater of Worlds is a difficult boss early game that gives a lot of players trouble. Master Mode gives him a large damage output that causes many people to die to him.
The best way to beat the Eater of Worlds on Master Mode is to use Molten Armor and a Molten Fury with Jester’s arrows.
There are also a few other things that you should know that will make the fight so easy you can repeatedly farm this boss.
Getting Hellstone early
Most people think you need to kill the Eater of Worlds to get a Nightmare Pickaxe, but in reality you only need to damage him for 6 Shadow Scales. Killing the Eye of Cthulhu one time should give you enough Demonite to make the pickaxe, which is all you need to get Hellstone.
Head to the Underworld and break the pots in the hell houses. Eventually, they’ll drop Obsidian Skin potions, which will allow you to survive in the lava. I found that I’m able to get around 300 Hellstone Ore with one single potion, but you should get 2 or 3 in case you die.
When you have Molten Armor and a Molten Fury, you’re close to being ready to fight the Eater of Worlds.
Preparing the arena
The arena for the Eater of Worlds should be located inside one of the chasms, and not on the surface. You don’t want to fight him on the surface, or else you’ll have to deal with the worm shooting projectiles at you.
Make a space underground and place platforms all around to grapple onto. Put some life regeneration accessories into the arena to give you an extra advantage as well. It would be even better if you used potions such as Iron Skin and a Regen Potion, but I didn’t need them in my fight.
Finishing the fight
When you have everything in place, craft a Worm Food to summon him straight to you. Dodge his initial attack and get above him, and shoot the Jester’s Arrows into his body. The purpose of Jester’s Arrows is to destroy his segments quickly and effectively.
Grapple from wall to wall to avoid his advanced. The only thing you need to watch out for is when his whole body surrounds you, so avoid that at all costs.
As his segments break up, he’ll attempt to shoot projectiles at you. Shoot the projectiles and get to work destroying the remaining segments. The bow and arrows will make quick work of him, and you should have arrows left over for another run.