// When Festering Newt dies, target creature an opponent controls gets -1/-1 until end of turn. That creature gets -4/-4 instead if you control a creature named Bogbrew Witch.
Effect effect = new ConditionalContinousEffect(
new BoostTargetEffect(-4,-4, Duration.EndOfTurn),
new BoostTargetEffect(-1,-1, Duration.EndOfTurn),
new LockedInCondition(new PermanentsOnTheBattlefieldCondition(filterBogbrewWitch)),
"target creature an opponent controls gets -1/-1 until end of turn. That creature gets -4/-4 instead if you control a creature named Bogbrew Witch");
Ability ability = new DiesTriggeredAbility(effect);
ability.addTarget(new TargetCreaturePermanent(filterCreature));
this.addAbility(ability);
}