my $sabal = new XML::Twig(        
              twig_roots          => {
                     'foo/yahoo'  =>
                     #'bayking[@id="kingtony"]'   =>
                         sub {  
                                my ($yabal, $element ) = @_;
                                if ( $element->first_child('bayking_li
+st')->first_child('bayking')->att('id') eq 'kingtony' ) {
                                       $element->print;
                             }
                          }
              }
);

$sabal->parse($xml);
[download]

<yahoo V="baz"><bay_id><value>1000</value><fact>yes</fact></bay_id><ba
+y_seen><value>50</value><fact>no</fact></bay_seen><bay_overall value=
+"disabled"/><bayking_list><bayking active="true" country="Russia" id=
+"kingtony"><bayking type="dictator"/><bay_usage value="none"/><baykin
+g_origin><bayking_origin_name emmigrate="no" value="ohio_usa"><econom
+y_status_previous value="very poor"/></bayking_origin_name></bayking_
+origin></bayking></bayking_list><bayqueen_list><bayqueen active="true
+" country="japan" id="queensarah"><bayqueen type="dictator"/><bay_usa
+ge value="none"/><bayqueen_origin><bayqueen_origin_name emmigrate="no
+" value="ca_usa"/><economy_status_previous value="very poor"/><previo
+us marriage="no"/></bayqueen_origin></bayqueen></bayqueen_list></yaho
+o>
[download]