Note that the discard is part of the effect, not a cost. So if you discard a Dark World monster whose effect activate when it is discarded from the hand to the Graveyard by a card effect, you'll get two benefits for the price of one.
Note that the discard is part of the effect, not a cost. So if you discard a Dark World monster whose effect activate when it is discarded from the hand to the Graveyard by a card effect, you'll get two benefits for the price of one.