Why are you using a temporary file at all? Couldn't you just read backward from each file and print to STDOUT?

something like

for my $file (reverse @ARGV) {
   read_backward_and_print($file);
}
[download]

Why do you need 2 arguments? I'd guess you might want to reverse a single file too...

I'd write your check as:

die "Usage: $0 FILENAMES\n" unless @ARGV >= 2;
[download]

Also, I was under the impression that tac was supposed to print the lines in the files in reverse order, NOT to also print the reverse of each line...