Another approach:

my $str = 'ABC---';
my $dash = $str =~ tr/-//d;
my %combo = ($str => 1);

%combo = map {
    my $x = $_;
    map {$x =~ s/.{$_}\K/-/r, 1} 0..length;
} keys %combo for 1..$dash;

say for reverse sort keys %combo;

__END__
ABC---
AB-C--
AB--C-
AB---C
A-BC--
A-B-C-
A-B--C
A--BC-
A--B-C
A---BC
-ABC--
-AB-C-
-AB--C
-A-BC-
-A-B-C
-A--BC
--ABC-
--AB-C
--A-BC
---ABC
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