// Kicker {B} (You may pay an additional {B} as you cast this spell.)
this.addAbility(new KickerAbility("{B}"));
// When Gatekeeper of Malakir enters the battlefield, if it was kicked, target player sacrifices a creature.
EntersBattlefieldTriggeredAbility ability =
new EntersBattlefieldTriggeredAbility(new SacrificeEffect(filter, 1, "target player"));
Ability conditionalAbility = new ConditionalTriggeredAbility(ability, KickedCondition.getInstance(), "When {this} enters the battlefield, if it was kicked, target player sacrifices a creature.");
conditionalAbility.addTarget(new TargetPlayer());
this.addAbility(conditionalAbility);
}