"Insanity" is a keyword that represents a continuous power that functions in all zones. The phrase "Insanity: <text>" means, "<text> is active only if this card started the game in an insane deck." This may add text inside an existing power or modifier, or may produce separate modifiers, depending on where the keyword appears.
A deck is "insane" if it has no more than one copy of each card. The first time each game a player reveals a card with the insanity keyword to an opponent, the player must announce whether or not their deck is insane.