Bone Serpent

The Bone Serpent is the strongest non-boss burrowing enemy, second only to the Eater of Worlds. They have a very small chance of dropping either a Flamelash or Sunfury and follow the Worm AI. Bone Serpents are immune to lava.

To make fighting them easier, try flooding The Underworld with a lot of water. This will cause the Bone Serpents to move slower through the water and thus easier to kill. The best way of killing one is the same as killing any other worm, by using weapons that can hit multiple enemies simultaneously like the Blade of Grass. Each section of a Bone Serpent can drop loot, but as they are usually defeated by destroying only one segment of their bodies, they seem to drop only one item. Causing a large amount of damage to multiple body sections at once with Dynamite will result in potential loot from every destroyed section. This can drastically increase the loot gained from Bone Serpents and is a great tactic when searching for the elusive Sunfury.

When fighting them it is recommended to have a lot of potions, end game armor and weapons to be able to stay alive for extensive periods of time.