The Wandering Eye Fish is a pre-Hardmodeenemy that can be spawned by fishing in a Blood Moon. When the bobber dips and the player attempts to reel in a fish, a Wandering Eye Fish or a Zombie Merman has a chance to spawn within a few blocks of the bobber in place of a fish.
It is one of the few entities that can be detected by the Lifeform Analyzer or its upgrades.
The Sonar Potion will detect if a Blood Moon enemy is about to be hooked.
Using the Chum Caster will greatly increase the chances of hooking Blood Moon enemies.
The Wandering Eye Fish has high health and defense, moves very quickly, and doesn't take knockback, making it a challenging enemy for underpowered characters.
It is recommended to avoid fishing in a Blood Moon while inside an enclosed space (like a building), as this may make escape difficult if the player is caught off guard.
One way to effectively fight the Wandering Eye Fish is to obtain a movement accessory such as a Cloud in a Bottle or Rocket Boots and make tight circles around the eye. Its top speed can easily outrun early-game players, but its turning radius is limited.
Unlike most flying enemies, the Wandering Eye Fish can enter water, though it will still be slowed down when submerged.
If the Wandering Eye Fish is afflicted with the Confused debuff, it may fly away far enough to despawn unless the player chases it.
A way to easily beat the Wandering Eye Fish relatively early in the game is to stomp it with a Slimy Saddle. Jumping on the Wandering Eye Fish with the saddle on will make it vertically lock on to the player, and it will quickly melt its own health bar by ramming itself into the mount. The player should take care to avoid falling to their death if they miss a stomp.
It has a similar appearance to Demon Eyes and Wandering Eyes, being named after the latter. Rather than severed nerves and blood vessels trailing from its rear, it sports red fins. It closely resembles The Fish of Cthulhu.
The Bestiary entry for the Wandering Eye Fish: "For mysterious reasons, fish are known to mutate with other living things or even man-made objects. This one is especially violent."