Moa

The Moa is a flying eyeball-like creature in The Adventure of Link. They typically fly either back and forth, or in a swooping fashion. Every time a Moa collides with Link, he loses not only a moderately large amount of health, but also a few experience points. The best way to defeat these flying creatures is to use either the Up or Down Thrust.

There are several varieties of the Moa, with varying strengths:

The Fire Moas are orange Moas that worth 100 experience points for killing; they are found mostly in dungeons and drop fireballs as they pass overhead. The Purple Moas are invisible, and can only be seen by finding the Cross.

Trivia
The Girubokku enemies from the same game greatly resemble Moas in being giant floating eyeballs. However, they fight rather differently, traveling around the screen for a short distance before opening their single great eye, which is Link's only opening to attack.