How to use

BecomesTargetControllerSpellTriggeredAbility

in

mage.abilities.common

@Override
public BecomesTargetControllerSpellTriggeredAbility copy() {
  return new BecomesTargetControllerSpellTriggeredAbility(this);
}

public DormantGomazoa(UUID ownerId, CardSetInfo setInfo) {
  super(ownerId,setInfo,new CardType[]{CardType.CREATURE},"{1}{U}{U}");
  this.subtype.add(SubType.JELLYFISH);
  this.power = new MageInt(5);
  this.toughness = new MageInt(5);
  this.addAbility(FlyingAbility.getInstance());
  // Dormant Gomazoa enters the battlefield tapped.
  this.addAbility(new EntersBattlefieldTappedAbility());
  // Dormant Gomazoa doesn't untap during your untap step.
  this.addAbility(new SimpleStaticAbility(Zone.BATTLEFIELD, new DontUntapInControllersUntapStepSourceEffect()));
  // Whenever you become the target of a spell, you may untap Dormant Gomazoa.
  this.addAbility(new BecomesTargetControllerSpellTriggeredAbility(new UntapSourceEffect(), true));
}