Zombie Merman

The Zombie Merman is a pre-Hardmode enemy that can be spawned by fishing in a Blood Moon. When the bobber dips and the player attempts to reel in a fish, a Zombie Merman or a Wandering Eye Fish has a chance to spawn within a few blocks of the bobber in place of a fish.

Tips

 * The Zombie Merman has high health and defense, moves very quickly, and doesn't take knockback, making it a challenging enemy for underpowered characters.
 * The Zombie Merman is very agile while in water, making it hard to deal with. Players can build a layer of platforms above their fishing spot to prevent the Zombie Merman from entering the water in the first place.
 * Despite not taking knockback, it will still briefly pause when hit like other enemies with 100% knockback resistance, making rapid fire weapons like the Minishark fairly effective at slowing it down.
 * The Zombie Merman is a great way of progressing in the early game as they can drop useful items, but be cautious, as an unprepared player can quickly be overwhelmed.

Trivia

 * The Zombie Merman Banner is the last item in alphabetical order out of all the items in Terraria.