Kill Effect

public abstract class KillEffects extends Cosmetics {

    public KillEffects(String subname, int id, int cost, String permission) {
        super(subname, id, cost, permission);
    }

    public abstract void start(GamePlayer gamePlayer);
}

Example.class

public class LightningKillEffect extends KillEffects {

    public LightningKillEffect() {
        super("Lightning Strike", 0, 100, "skywars.cosmetics.effect.lightning");
    }

    @Override
    public void start(GamePlayer gamePlayer) {
        Location location = gamePlayer.getLocation();
        location.getWorld().strikeLightningEffect(location);
        gamePlayer.sendSound("ENTITY_LIGHTNING_BOLT_IMPACT");
    }
}