// As Entropic Specter enters the battlefield, choose an opponent.
this.addAbility(new AsEntersBattlefieldAbility(new ChooseOpponent()));
// Entropic Specter's power and toughness are each equal to the number of cards in the chosen player's hand.
this.addAbility(new SimpleStaticAbility(Zone.ALL, new SetPowerToughnessSourceEffect(new CardsInTargetPlayerHandCount(), Duration.WhileOnBattlefield)));
// Whenever Entropic Specter deals damage to a player, that player discards a card.
this.addAbility(new DealsDamageToAPlayerTriggeredAbility(new DiscardTargetEffect(1, false), false, true));
}