<===> input.scss
@mixin foo($x, $y, $zs...) {
  foo-x: $x;
  foo-y: $y;
  foo-zs: $zs;
}

div {
  @include foo(a, b, c, d, e);
}
<===> output.css
div {
  foo-x: a;
  foo-y: b;
  foo-zs: c, d, e;
}