pocketmine\entity\Human::setSkin PHP Method

    public function setSkin($str, $skinId)
    {
        $this->skin = $str;
        $this->skinId = $skinId;
    }

 public function setSkin($str, $skinname = "", $isOldClient = false, $isSlim = false, $isTransparent = null)
 {
     parent::setSkin($str, $skinname, $isOldClient, $isSlim, $isTransparent);
     if ($this->spawned) {
         $this->server->sendFullPlayerListData($this);
     }
 }