Fish Eye is part of the Amazon Trio. All of their dream-mirror sequences are the same. They shout "One!" ::backboard comes up on victim:: "Two!" ::victim is locked down:: "Three!" ::dream-mirrors come out:: Pretty nifty, eh? The members of the Amazon Trio were originally animals who had been turned into humans. Since they weren't humans, they had no dreams, no dream-mirrors. Fish Eye was once a fish, hence his name. Being a fish, he's scared to death of cats.
In the Dead Moon Circus, Fish Eye is an acrobat. You usually saw him balancing on giant balls. He also threw knives (badly) in this one episode. His (and the Amazon Trio's) job is to find the holder who had Pegasus in his/her dream-mirror, because with Pegasus came the Golden Crystal on his horn; the crystal that would enable Nehelenia to take over the world and for the Amazon Trio to remain human. The Amazon Trio selects their victims by looking at pictures of potential victims. Sometimes their boss Zirconia gets fed up with them, however, and selects victims for them :).
Fish Eye is very feminine. He prefers to dress in female clothes when in "civilian" form, and his targets are men. Any age. Once, Fish Eye even attacked a boy from Chibiusa's school 0_o! Fish Eye usually falls in love with his victims and seeks their love before attacking. It usually lasts only until the victim's dream-mirror is checked, Mamoru excepting. Unrequited love is the reason for most of his attacks, in my opinion ;).
Fish Eye was the first of the Amazon Trio to question Zirconia. He wanted to know why he had no dreams (still hung up on the fact that Mamoru's sweetie is a "girl with many dreams"). I believe that Fish Eye led to the rebellion of the Amazon Trio. He was willing to use the last of their powers to save Sailor Moon, and convinced the others as well. What a selfless guy. One of my friends ScandiaDream once asked which villian was the most full of love, and while I answered 'Safiru', SailorPsychosis answered 'Fish Eye'. Now that I think about it, Psychosis is exactly right (and I feel so ashamed for picking someone I despise vs. my darling Fish!). Fish Eye was willing to sacrifice himself for a person that he only knew slightly through Mamoru. I think that was very sweet of him. But anyway, as a result of giving up the last of their power, the Amazon Trio die, but Pegasus revives them and gives them the ability to dream, Fish Eye's biggest dream of all.