The second element in @values is already an array reference. In the first line of your sub, you are assigning the number of elements in @_, not the first element itself. Your code can be simplified as follows:

my @values=([some,things] , [1,2,3,4,5,6]);
my ($a, $b, $c, $d) = CalcMinAvgMaxSum( $values[1]);
sub CalcMinAvgMaxSum()
{
    my $ArrayOfValues_REF = shift;
    for my $val (@{$ArrayOfValues_REF})
    {
         print "$val\n";
    }
}
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