Whenever an opponent discards a card, Abyssal Nocturnus gets +2/+2 and gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.)
2/1/2006 If your opponent discards any cards during their cleanup step to get down to the maximum hand size, the ability will trigger and players will receive priority. After that cleanup step ends, a new one will begin and Abyssal Nocturnus’s effect will end. It won’t carry over into the next turn.
2/1/2006 If your opponent discards multiple cards to a single effect, this will trigger multiple times.