The ZIlch was added in the 4th expansion by Eon Productions, ostensibly in an attempt to add a potential 7th or 8th player to the game.
You have the power to kibitz. You get no hex, tokens, cards etc. At the start of the game you write down the player you think will win. If at the end of the game, he is a winner, you win instead. To help you mold the outcome, you may look at anything in the game at any time: hands, hidden powers, secret writings, the Deck, etc. You may tell anyone anything you like, publicly or privately, including lies. And you are not affected by any power or card except the "Cosmic Zap"
Wild Flare - You may look at any gaming components for ten seconds. Discard after use.
Super Flare - You may change your decision about which player will win. Discard after use.
Note that the super flare makes no sense, because the Zilch has no hand and thus can never have this card.
I don't know who made up the above information, but the original Shark and Zilch do not have flares.
Created at the same time as the Shark, this is a player who doesn't really get to play. Instead you just get to annoy the other players and try to mislead them as to who you really want to be victorious. One extremely bad aspect of the Zilch is that the hapless player whom you picked cannot win the game, which is pretty sucky.