this.color.setBlack(true);
DynamicValue xValue = new SignInversionDynamicValue(new GetXValue());
// {B}, Remove X +1/+1 counters from among creatures you control: Target creature gets -X/-X until end of turn.
Ability ability = new SimpleActivatedAbility(Zone.BATTLEFIELD, new BoostTargetEffect(xValue,xValue,Duration.EndOfTurn, true), new ManaCostsImpl("{B}"));
ability.addCost(new RemoveVariableCountersTargetCost(filter, CounterType.P1P1, "X", 0));
ability.addTarget(new TargetCreaturePermanent());
this.addAbility(ability);
}