Aquamentus is the supereasy boss of Level 1 and Level 7 of the Legend of Zelda. Although to myself, and most other Americans, Aquamentus looks somewhat like a dragon, he is actually a unicorn, or perhaps a kirin.
Even in the first Level, Aquamentus is quite easy to defeat. When he appears at the end of Level 7, at which time Link can walk through a pack of angry centaurs without a scratch, fighting him is anticlimactic to say the least.
The name "aquamentus" means "Water Mind" or perhaps "Water Spirit", although for what reason I do not know. Both of the levels he is in are reached by water, but there is nothing particularly aquatic about him (or her).