Destiny\Advisors\Activity::addActiveSkulls PHP Method

    public function addActiveSkulls(ActivityDefinition $definition, array $skulls)
    {
        $activitySkulls = $definition->getNonMutatedProperty('skulls');
        if (is_array($activitySkulls)) {
            foreach ($activitySkulls as $key => $skull) {
                if (!in_array($key, $skulls)) {
                    unset($definition->properties['skulls'][$key]);
                }
            }
        }
        $this->skulls = $definition->getNonMutatedProperty('skulls');
    }

 protected function gNightfall()
 {
     $nightfall = $this->getNonMutatedProperty('nightfall');
     if ($nightfall == null) {
         return null;
     }
     $definition = manifest()->activity($nightfall['specificActivityHash']);
     $skulls = manifest()->activity($nightfall['activityBundleHash']);
     $activity = new Advisors\Activity($this, $definition, $this->nightfallResetDate);
     $activity->addLevelRewards($skulls);
     $activity->addActiveSkulls($skulls, $nightfall['tiers'][0]['skullIndexes']);
     return $activity;
 }