The Eater of Worlds is a pre-Hardmode Corruption boss made of many connected segments. It can appear after every third Shadow Orb is destroyed or be summoned with Worm Food in the Corruption.
Why the segmented body matters
Each segment has its own health. Destroying an inner segment can split the boss into smaller worms, so attacks that hit several body parts at once may create much more value than narrow single-target attacks.
Arena preparation
Create enough space in the Corruption to move vertically and horizontally without getting trapped by terrain. Platforms can help you keep distance while still allowing the worm to pass through the arena.
Fight priorities
- Keep moving instead of standing where multiple segments can overlap you.
- Use attacks that can hit several segments when your loadout supports it.
- Watch for smaller worms after the boss splits.
- Keep healing ready for moments when several segments cross your position at once.
Progression context
The Eater of Worlds is part of Corruption progression and can be used as an early checkpoint for whether your equipment and mobility are ready for later pre-Hardmode content.
Source: Official Terraria Wiki.