Hemogoblin Shark

The Hemoglobin Shark is a Hardmode enemy that can be spawned by fishing during a Blood Moon event. When the bobber dips and the player attempts to reel in a fish, a Hemoglobin Shark or another enemy has a chance to spawn in place of a fish, within a few blocks of the bobber. It can move incredibly fast in water, can jump very high, and has a suprising amount of health, so it is not an enemy to be trifled with on any difficulty setting.

Trivia

 * The name 'Hemogoblin Shark' is a portmanteau of "hemoglobin", an oxygen-carrying protein found in vertebrates which is responsible for giving blood its red color, and "goblin shark," a rare and ancient species of shark native to deep waters of the Eastern Atlantic.
 * The Hemogoblin Shark's Bestiary entry — "Half-shark, half-goblin, completely murderous!" — references the Minishark's tooltip.