Yeah, I'd go with the unpack and a slice.

my @arr = qw( and you will be pleased with the results );
my $mask = 0x2b;

sub mask_array (\@$) {
  my( $arr, $mask ) = @_;
  my @want = split '', unpack( "b*", $mask );
  return @{ $arr }[ grep { $want[ $_ ] } 0..$#{ $arr } ];
}

my @result = mask_array @arr => $mask;
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Update: Hypothetically you could use return @{ $arr }[ grep { vec( $mask, $_, 1 ) } 0..$#{ $arr } ] instead of making @want, but I'd bet that's a little slower than the above version.