// {tap}: Gain control of target creature whose controller controls an Island for as long as you control Seasinger and Seasinger remains tapped.
ConditionalContinousEffect effect = new ConditionalContinousEffect(
new GainControlTargetEffect(Duration.Custom),
new PermanentsOnTheBattlefieldCondition(seasinger, PermanentsOnTheBattlefieldCondition.CountType.EQUAL_TO, 1, SourceTappedCondition.getInstance()), rule);
Ability ability = new SimpleActivatedAbility(Zone.BATTLEFIELD, effect, new TapSourceCost());
creatureWhoseControllerControlsIsland.add(new ControllerControlsIslandPredicate());
ability.addTarget(new TargetCreaturePermanent(creatureWhoseControllerControlsIsland));
this.addAbility(ability);
}