How do I render a form?
drupal_get_form() has been replaced by the form builder service, e.g.:

$form = \Drupal::formBuilder()-&gt;getForm(\Drupal\user\Form\UserLoginForm::class);


See the Change Record for more details.

Actually, don't - that change record is incorrect. It'll tell you to pass the form ID, when in fact you need to pass the class string.