Updated >= Drupal 8.0.5+: Rendering forms/entities programmatically on theming level
I'm still new to drupal but here is what i did to render a form in node.html.twig:

//file themename.theme
function themename_preprocess_node(&amp;$variables) {
  if(isset($variables['node'])){
    $node = $variables['node'];
    if($node-&gt;getType() == 'application') {
        $message = \Drupal::entityTypeManager()
            -&gt;getStorage('contact_message')
            -&gt;create(array(
            'contact_form' =&gt; 'webentwickler_job', //ID(Machine name) of form
        ));
        $form = \Drupal::service('entity.form_builder')-&gt;getForm($message);
        $variables['application_form'] = $form;
    }
  }
}

//file node--application.html.twig
{{ application_form }}