Effect effect = new BoostTargetEffect(xValue,xValue,Duration.EndOfTurn);
effect.setText("Target creature gets -X/-X until end of turn");
Ability ability = new SimpleActivatedAbility(Zone.BATTLEFIELD, effect, new ManaCostsImpl("{X}"));
ability.addCost(new TapSourceCost());
ability.addTarget(new TargetCreaturePermanent());
ability.addCost(new ExileFromGraveCost(new TargetCardInYourGraveyard(1,1,new FilterCard("cards from your graveyard")), "Exile X cards from your graveyard"));
this.addAbility(ability);
}