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.

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.

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.