#!usr/bin/perl
use strict;
use warnings;

use Data::Dumper;

my @x = [100, 101];  #may not be what you want?
print Dumper \@x;

my @dead_list = (100,
            101,
            103,
            200,
            201,
            202,
            203,
            210,
            211,
            212,
            220,
            221,
            222,
            230,
            231,
            232,
            233,
            240,
            241,
            242,
            243,
            1000,
            1001,
            1002,
            1010,
            1011,
            1012,
            1020,
            1021,
            1022,
            1120,
            1121,
            1122,
            1210,
            1211,
            1212);
            
my @get_list   = (
            '100',
            '200',
            '210',
            '220',
            '230',
            '240',
            '1000',
            '1001',
            '1002',
            '1120',
            '1210',);

sub remove_x99
{
   my ($deadlist_ref, $getlist_ref) = @_;
   
   my %lookup = map{$_=>1}@$getlist_ref;
   my @result = grep{!exists $lookup{$_}}@$deadlist_ref;
   
   return @result;
}

my @result = remove_x99 (\@dead_list, \@get_list);
print "@result\n";

__END__
$VAR1 = [
          [
            100,
            101
          ]
        ];
101 103 201 202 203 211 212 221 222 231 232 233 241 242 243 1010 1011 1012 1020 1021 1022 1121 1122 1211 1212

Note: in the sub if you wanted to modify dead_list:
@$deadlist_ref = grep{!exists $lookup{$_}}@$deadlist_ref;
would do that.