// Bestow 3UU (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
this.addAbility(new BestowAbility(this, "{3}{U}{U}"));
// When Crystalline Nautilus becomes the target of a spell or ability, sacrifice it.
this.addAbility(new BecomesTargetTriggeredAbility(new SacrificeSourceEffect()));
// Enchanted creature gets +4/+4 and has "When this creature becomes the target of a spell or ability, sacrifice it."
Effect effect = new BoostEnchantedEffect(4,4,Duration.WhileOnBattlefield);
effect.setText("Enchanted creature gets +4/+4");
Ability ability = new SimpleStaticAbility(Zone.BATTLEFIELD, effect);
effect = new GainAbilityAttachedEffect(new BecomesTargetTriggeredAbility(new SacrificeSourceEffect()), AttachmentType.AURA, Duration.WhileOnBattlefield);
effect.setText("and has \"When this creature becomes the target of a spell or ability, sacrifice it.\"");
ability.addEffect(effect);
this.addAbility(ability);
}