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.

Varieties
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.

Captain N: The Game Master
Moas appear in the "Quest for the Potion of Power" episode of Captain N: The Game Master. While Link, Princess Zelda, and Kevin are in a graveyard, a large group of Moas suddenly appear. Although the heroes are successful in defeating various Moas, they decide to run away as they cannot hope to defeat all of them, and they leave the Moa-infested graveyard via a tunnel that leads to the Island Palace.

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.