Here is a way using the sort ..
You do not need @arr2 .

use strict;

my (@arr1);

$arr1[0] = "john:::10";
$arr1[1] = "bill:::9";
$arr1[2] = "mary:::35";
$arr1[3] = "willy:::21";

#####################

sub comparesimple {
    (split /:/,$a)[-1] # Take last element of split..
     <=>               # Do numeric compare   
   (split /:/,$b )[-1]

}
##############################
print qq($_ \n) for sort comparesimple @arr1;
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