'The' Shell King is a turtle-like boss that can be summoned with the Giant Turtle Shell. It has several attack styles. The Shell King has 14,000 Heart.

First stage

In the first stage of the fight, the Shell King will remain inside its shell and be invincible. It will occasionally poke its head out, at which point it can be damaged. It will primarily attack by spinning around and then slamming into the player quickly; this attack has a base 200 power. While undergoing this attack, the Shell King can be damaged, but for 1/4 of the normal damage done to it. Its second stage can be unlocked by bringing it down to 7,000 Heart.

Second stage

In its second stage, the Shell King does a base damage of 400 with its shell attack, but will not stick its head into its shell anymore. It will also run slowly at the player for a damage of 100.