You still have tied($arr_ref) to get your scalar reference

Indeed I do. Mmmmm, I can work with that. Thanks!

This more or less does the trick:

package TwoFaced;
use strict;
my $instance_counter = 0;
my $instance_array   = [];

sub new {
    my $class = shift;
    my @array;
    tie @array, $class, @_;
    return bless \@array, $class;
}

sub method {
    print "Method call\n";
    return;
}

sub TIEARRAY {
    my ( $class, @args ) = @_; 
    my $self = $instance_counter++;      
    return bless \$self, $class;
}

sub FETCH {
    my ( $self, $i ) = @_;
    return $instance_array->[ $$self ]->[$i];
}

sub STORE {
    my ( $self, $i, $val ) = @_;
    if ( not $val eq 'a' ) {
        $instance_array->[ $$self ]->[$i] = $val;
        return $self;
    }
    else {
        die "Illegal value: $val\n";
    }
}

sub FETCHSIZE {
    my ( $self ) = @_;
    return scalar @{ $instance_array->[ $$self ] };
}

sub DESTROY {
    print "Contents at death:\n";
    print "\t", $_, "\n" for @{ $instance_array->[ $$_[0] ] };
}

package main;
my $t = new TwoFaced;
print "it's an array!\n" if UNIVERSAL::isa($t, 'ARRAY'); # prints "it'
+s an array!";

$t->[0] = 'b';
print ${ tied @$t }, $t->[0]; # prints "0b"
print $t->method;             # prints "Method call"
$t->[0] = 'a';                # dies "Illegal value: a"
# prints "Contents at death: ..." during object destruction
[download]

...except the destructor is called twice. I presume this is for the @array and the tied object respectively?