Wolfduck is a boss from the NES Darkwing Duck game. He is a supervillain duck who transforms whenever the moon is full and showing, returning to his slim self when it gets covered.
According to the game's story, FOWL's activities have prompted many supervillains to start a crime spree around St. Cannard. Wolfduck and his henchmen started rampaging at the center of the city, so Darkwing Duck goes there to fight him.
The battle with Wolfduck involves him bulking up when the moon gets full, then tossing a large box at DW, after which the moon gets covered by clouds and thus Wolfduck loses his strength, running around the arena. He is only vulnerable when he is depowered, though he can still hurt the player.