Heater of Worlds

Not to be confused with the Eater of Worlds, a vanilla boss with a similar name.

Heater of Worlds is a Pre-Hardmode boss fought in the Underworld.

Spawn
The Heater of Worlds doesn't spawn on its own. The only way to summon it is to use a Molten Heart. It can be used anywhere in the Underworld.

Behavior
Burrows through blocks like standard worm enemies, faster than sprinting speed. Only its head segment can be damaged.

Attacks

 * Each body segment occasionally releases a spark of flame that has a slight bounce and remains on the ground for a few seconds. Each fireball does half contact damage.
 * Can summon Magma Leeches minions that burrow through blocks like Heater of Worlds itself.

Expert mode

 * Contact with Heater of Worlds and Magma Leeches inflcits On Fire! debuff for 3 seconds.

Tips

 * This boss can easily be rendered ineffectual by creating a thin land bridge between two large masses of Ash Blocks. Have it burrow through one mass to gain enough speed to reach your height, then simply dodge it and take your shots at the tail. Staying out on the bridge will leave you out of its reach, unless it burrows at a perfect angle to travel through the bridge. This is your best chance to do the most damage, just remember that it WILL catch up.