Zombie Merman

The Zombie Merman is a pre-Hardmode enemy which can be spawned by fishing in a Blood Moon. When the bobber dips and a player clicks to reel in a fish, a Zombie Merman or a Wandering Eye Fish has a chance to spawn in place of a fish, within a few blocks to either side of the bobber. These two enemies drop various useful items, including the Vampire Frog Staff and the Chum Caster.

Tips

 * The Zombie Merman has high health and defense, and it also doesn't take knockback, so underpowered characters should beware.
 * 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 somewhat effective at slowing it down.
 * The Zombie Merman could be a great way of getting some better loot in the early game as they can drop some useful weapons but be cautious as an unprepared player might get overpowered.