The following is a failing test that demonstrates the problem. I would go ahead and extend it further to additional examples. Then, you now have something to write your plugin against.

use Test::More tests => 1;

use DBM::Deep;
use Data::Compare;

use File::Temp qw( tempfile );

my $filename = tempfile();

my $db = DBM::Deep->new( file => $filename );
$db->{foo} = [ 1 .. 3 ];

my $compare = {
    foo => [ 1 .. 3 ],
};

ok( Compare( $db, $compare ), "The structures are the same" );
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Now, you also have an excellent example plugin with [src://Data::Compare::Plugins::Scalar::Properties]. You could copy that module, rename it, and change sp_scalar_compare to dbm_scalar_compare and change its logic a bit. At that point, you can run your test and see if anything passes. At that point, you can hand it to me and we can work with something. Remember - the hardest part is the blank page. Editing is sooo much easier than creating.