Bone Serpent

The Bone Serpent is the strongest non-boss burrowing enemy. Every part except the tail and the head has 150 HP, and the tail has 200 HP and the head 120 HP. They can move through any block, and are not affected by lava or drowning. Destroying one part of a Bone Serpent will kill it. It has a very rare chance of dropping a Flamelash or a Sunfury, one of the strongest weapons in the game. The only more powerful burrowing enemy is the Eater of Worlds, which is a boss.