<===> input.scss
$list: ("a", "b", "c");

test {
    content: nth($list, -1);
    content: nth($list, -2);
    content: nth($list, -3);
    content: nth($list, -1) == nth($list, length($list));
}

<===> output.css
test {
  content: "c";
  content: "b";
  content: "a";
  content: true;
}