use strict;
use warnings;
use 5.014;  
use Data::Dumper;

my %hash = ('hello', 1, 'goodbye', 2, 'world', 3, 'mars', 4);
@hash{'goodbye', 'world'} = ();

say Dumper(\%hash);

--output:--
$VAR1 = {
          'mars' => 4,
          'hello' => 1,
          'world' => undef,
          'goodbye' => undef
        };